December 2025 - Linux-stable-mirror

[PATCH RESEND v3 4/4] mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather

by David Hildenbrand (Red Hat)

As reported, ever since commit 1013af4f585f ("mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race") we can end up in some situations where we perform so many IPI broadcasts when unsharing hugetlb PMD page tables that it severely regresses some workloads. In particular, when we fork()+exit(), or when we munmap() a large area backed by many shared PMD tables, we perform one IPI broadcast per unshared PMD table. There are two optimizations to be had: (1) When we process (unshare) multiple such PMD tables, such as during exit(), it is sufficient to send a single IPI broadcast (as long as we respect locking rules) instead of one per PMD table. Locking prevents that any of these PMD tables could get reused before we drop the lock. (2) When we are not the last sharer (> 2 users including us), there is no need to send the IPI broadcast. The shared PMD tables cannot become exclusive (fully unshared) before an IPI will be broadcasted by the last sharer. Concurrent GUP-fast could walk into a PMD table just before we unshared it. It could then succeed in grabbing a page from the shared page table even after munmap() etc succeeded (and supressed an IPI). But there is not difference compared to GUP-fast just sleeping for a while after grabbing the page and re-enabling IRQs. Most importantly, GUP-fast will never walk into page tables that are no-longer shared, because the last sharer will issue an IPI broadcast. (if ever required, checking whether the PUD changed in GUP-fast after grabbing the page like we do in the PTE case could handle this) So let's rework PMD sharing TLB flushing + IPI sync to use the mmu_gather infrastructure so we can implement these optimizations and demystify the code at least a bit. Extend the mmu_gather infrastructure to be able to deal with our special hugetlb PMD table sharing implementation. To make initialization of the mmu_gather easier when working on a single VMA (in particular, when dealing with hugetlb), provide tlb_gather_mmu_vma(). We'll consolidate the handling for (full) unsharing of PMD tables in tlb_unshare_pmd_ptdesc() and tlb_flush_unshared_tables(), and track in "struct mmu_gather" whether we had (full) unsharing of PMD tables. Because locking is very special (concurrent unsharing+reuse must be prevented), we disallow deferring flushing to tlb_finish_mmu() and instead require an explicit earlier call to tlb_flush_unshared_tables(). From hugetlb code, we call huge_pmd_unshare_flush() where we make sure that the expected lock protecting us from concurrent unsharing+reuse is still held. Check with a VM_WARN_ON_ONCE() in tlb_finish_mmu() that tlb_flush_unshared_tables() was properly called earlier. Document it all properly. Notes about tlb_remove_table_sync_one() interaction with unsharing: There are two fairly tricky things: (1) tlb_remove_table_sync_one() is a NOP on architectures without CONFIG_MMU_GATHER_RCU_TABLE_FREE. Here, the assumption is that the previous TLB flush would send an IPI to all relevant CPUs. Careful: some architectures like x86 only send IPIs to all relevant CPUs when tlb->freed_tables is set. The relevant architectures should be selecting MMU_GATHER_RCU_TABLE_FREE, but x86 might not do that in stable kernels and it might have been problematic before this patch. Also, the arch flushing behavior (independent of IPIs) is different when tlb->freed_tables is set. Do we have to enlighten them to also take care of tlb->unshared_tables? So far we didn't care, so hopefully we are fine. Of course, we could be setting tlb->freed_tables as well, but that might then unnecessarily flush too much, because the semantics of tlb->freed_tables are a bit fuzzy. This patch changes nothing in this regard. (2) tlb_remove_table_sync_one() is not a NOP on architectures with CONFIG_MMU_GATHER_RCU_TABLE_FREE that actually don't need a sync. Take x86 as an example: in the common case (!pv, !X86_FEATURE_INVLPGB) we still issue IPIs during TLB flushes and don't actually need the second tlb_remove_table_sync_one(). This optimized can be implemented on top of this, by checking e.g., in tlb_remove_table_sync_one() whether we really need IPIs. But as described in (1), it really must honor tlb->freed_tables then to send IPIs to all relevant CPUs. Notes on TLB flushing changes: (1) Flushing for non-shared PMD tables We're converting from flush_hugetlb_tlb_range() to tlb_remove_huge_tlb_entry(). Given that we properly initialize the MMU gather in tlb_gather_mmu_vma() to be hugetlb aware, similar to __unmap_hugepage_range(), that should be fine. (2) Flushing for shared PMD tables We're converting from various things (flush_hugetlb_tlb_range(), tlb_flush_pmd_range(), flush_tlb_range()) to tlb_flush_pmd_range(). tlb_flush_pmd_range() achieves the same that tlb_remove_huge_tlb_entry() would achieve in these scenarios. Note that tlb_remove_huge_tlb_entry() also calls __tlb_remove_tlb_entry(), however that is only implemented on powerpc, which does not support PMD table sharing. Similar to (1), tlb_gather_mmu_vma() should make sure that TLB flushing keeps on working as expected. Further, note that the ptdesc_pmd_pts_dec() in huge_pmd_share() is not a concern, as we are holding the i_mmap_lock the whole time, preventing concurrent unsharing. That ptdesc_pmd_pts_dec() usage will be removed separately as a cleanup later. There are plenty more cleanups to be had, but they have to wait until this is fixed. Fixes: 1013af4f585f ("mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race") Reported-by: Uschakow, Stanislav" <suschako(a)amazon.de> Closes: https://lore.kernel.org/all/4d3878531c76479d9f8ca9789dc6485d@amazon.de/ Tested-by: Laurence Oberman <loberman(a)redhat.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: David Hildenbrand (Red Hat) <david(a)kernel.org> --- include/asm-generic/tlb.h | 77 +++++++++++++++++++++++- include/linux/hugetlb.h | 15 +++-- include/linux/mm_types.h | 1 + mm/hugetlb.c | 123 ++++++++++++++++++++++---------------- mm/mmu_gather.c | 33 ++++++++++ mm/rmap.c | 25 +++++--- 6 files changed, 208 insertions(+), 66 deletions(-) diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h index 1fff717cae510..4d679d2a206b4 100644 --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -46,7 +46,8 @@ * * The mmu_gather API consists of: * - * - tlb_gather_mmu() / tlb_gather_mmu_fullmm() / tlb_finish_mmu() + * - tlb_gather_mmu() / tlb_gather_mmu_fullmm() / tlb_gather_mmu_vma() / + * tlb_finish_mmu() * * start and finish a mmu_gather * @@ -364,6 +365,20 @@ struct mmu_gather { unsigned int vma_huge : 1; unsigned int vma_pfn : 1; + /* + * Did we unshare (unmap) any shared page tables? For now only + * used for hugetlb PMD table sharing. + */ + unsigned int unshared_tables : 1; + + /* + * Did we unshare any page tables such that they are now exclusive + * and could get reused+modified by the new owner? When setting this + * flag, "unshared_tables" will be set as well. For now only used + * for hugetlb PMD table sharing. + */ + unsigned int fully_unshared_tables : 1; + unsigned int batch_count; #ifndef CONFIG_MMU_GATHER_NO_GATHER @@ -400,6 +415,7 @@ static inline void __tlb_reset_range(struct mmu_gather *tlb) tlb->cleared_pmds = 0; tlb->cleared_puds = 0; tlb->cleared_p4ds = 0; + tlb->unshared_tables = 0; /* * Do not reset mmu_gather::vma_* fields here, we do not * call into tlb_start_vma() again to set them if there is an @@ -484,7 +500,7 @@ static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb) * these bits. */ if (!(tlb->freed_tables || tlb->cleared_ptes || tlb->cleared_pmds || - tlb->cleared_puds || tlb->cleared_p4ds)) + tlb->cleared_puds || tlb->cleared_p4ds || tlb->unshared_tables)) return; tlb_flush(tlb); @@ -773,6 +789,63 @@ static inline bool huge_pmd_needs_flush(pmd_t oldpmd, pmd_t newpmd) } #endif +#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING +static inline void tlb_unshare_pmd_ptdesc(struct mmu_gather *tlb, struct ptdesc *pt, + unsigned long addr) +{ + /* + * The caller must make sure that concurrent unsharing + exclusive + * reuse is impossible until tlb_flush_unshared_tables() was called. + */ + VM_WARN_ON_ONCE(!ptdesc_pmd_is_shared(pt)); + ptdesc_pmd_pts_dec(pt); + + /* Clearing a PUD pointing at a PMD table with PMD leaves. */ + tlb_flush_pmd_range(tlb, addr & PUD_MASK, PUD_SIZE); + + /* + * If the page table is now exclusively owned, we fully unshared + * a page table. + */ + if (!ptdesc_pmd_is_shared(pt)) + tlb->fully_unshared_tables = true; + tlb->unshared_tables = true; +} + +static inline void tlb_flush_unshared_tables(struct mmu_gather *tlb) +{ + /* + * As soon as the caller drops locks to allow for reuse of + * previously-shared tables, these tables could get modified and + * even reused outside of hugetlb context, so we have to make sure that + * any page table walkers (incl. TLB, GUP-fast) are aware of that + * change. + * + * Even if we are not fully unsharing a PMD table, we must + * flush the TLB for the unsharer now. + */ + if (tlb->unshared_tables) + tlb_flush_mmu_tlbonly(tlb); + + /* + * Similarly, we must make sure that concurrent GUP-fast will not + * walk previously-shared page tables that are getting modified+reused + * elsewhere. So broadcast an IPI to wait for any concurrent GUP-fast. + * + * We only perform this when we are the last sharer of a page table, + * as the IPI will reach all CPUs: any GUP-fast. + * + * Note that on configs where tlb_remove_table_sync_one() is a NOP, + * the expectation is that the tlb_flush_mmu_tlbonly() would have issued + * required IPIs already for us. + */ + if (tlb->fully_unshared_tables) { + tlb_remove_table_sync_one(); + tlb->fully_unshared_tables = false; + } +} +#endif /* CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING */ + #endif /* CONFIG_MMU */ #endif /* _ASM_GENERIC__TLB_H */ diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 03c8725efa289..e51b8ef0cebd9 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -240,8 +240,9 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma, pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr, unsigned long sz); unsigned long hugetlb_mask_last_page(struct hstate *h); -int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long addr, pte_t *ptep); +int huge_pmd_unshare(struct mmu_gather *tlb, struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep); +void huge_pmd_unshare_flush(struct mmu_gather *tlb, struct vm_area_struct *vma); void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, unsigned long *start, unsigned long *end); @@ -300,13 +301,17 @@ static inline struct address_space *hugetlb_folio_mapping_lock_write( return NULL; } -static inline int huge_pmd_unshare(struct mm_struct *mm, - struct vm_area_struct *vma, - unsigned long addr, pte_t *ptep) +static inline int huge_pmd_unshare(struct mmu_gather *tlb, + struct vm_area_struct *vma, unsigned long addr, pte_t *ptep) { return 0; } +static inline void huge_pmd_unshare_flush(struct mmu_gather *tlb, + struct vm_area_struct *vma) +{ +} + static inline void adjust_range_if_pmd_sharing_possible( struct vm_area_struct *vma, unsigned long *start, unsigned long *end) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 42af2292951d4..d1053b2c1f800 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1522,6 +1522,7 @@ static inline unsigned int mm_cid_size(void) struct mmu_gather; extern void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm); extern void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm); +void tlb_gather_mmu_vma(struct mmu_gather *tlb, struct vm_area_struct *vma); extern void tlb_finish_mmu(struct mmu_gather *tlb); struct vm_fault; diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 3c77cdef12a32..2609b6d58f99e 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5096,7 +5096,7 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, unsigned long last_addr_mask; pte_t *src_pte, *dst_pte; struct mmu_notifier_range range; - bool shared_pmd = false; + struct mmu_gather tlb; mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, old_addr, old_end); @@ -5106,6 +5106,7 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, * range. */ flush_cache_range(vma, range.start, range.end); + tlb_gather_mmu_vma(&tlb, vma); mmu_notifier_invalidate_range_start(&range); last_addr_mask = hugetlb_mask_last_page(h); @@ -5122,8 +5123,7 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, if (huge_pte_none(huge_ptep_get(mm, old_addr, src_pte))) continue; - if (huge_pmd_unshare(mm, vma, old_addr, src_pte)) { - shared_pmd = true; + if (huge_pmd_unshare(&tlb, vma, old_addr, src_pte)) { old_addr |= last_addr_mask; new_addr |= last_addr_mask; continue; @@ -5134,15 +5134,16 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, break; move_huge_pte(vma, old_addr, new_addr, src_pte, dst_pte, sz); + tlb_remove_huge_tlb_entry(h, &tlb, src_pte, old_addr); } - if (shared_pmd) - flush_hugetlb_tlb_range(vma, range.start, range.end); - else - flush_hugetlb_tlb_range(vma, old_end - len, old_end); + tlb_flush_mmu_tlbonly(&tlb); + huge_pmd_unshare_flush(&tlb, vma); + mmu_notifier_invalidate_range_end(&range); i_mmap_unlock_write(mapping); hugetlb_vma_unlock_write(vma); + tlb_finish_mmu(&tlb); return len + old_addr - old_end; } @@ -5161,7 +5162,6 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, unsigned long sz = huge_page_size(h); bool adjust_reservation; unsigned long last_addr_mask; - bool force_flush = false; WARN_ON(!is_vm_hugetlb_page(vma)); BUG_ON(start & ~huge_page_mask(h)); @@ -5184,10 +5184,8 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, } ptl = huge_pte_lock(h, mm, ptep); - if (huge_pmd_unshare(mm, vma, address, ptep)) { + if (huge_pmd_unshare(tlb, vma, address, ptep)) { spin_unlock(ptl); - tlb_flush_pmd_range(tlb, address & PUD_MASK, PUD_SIZE); - force_flush = true; address |= last_addr_mask; continue; } @@ -5303,14 +5301,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, } tlb_end_vma(tlb, vma); - /* - * There is nothing protecting a previously-shared page table that we - * unshared through huge_pmd_unshare() from getting freed after we - * release i_mmap_rwsem, so flush the TLB now. If huge_pmd_unshare() - * succeeded, flush the range corresponding to the pud. - */ - if (force_flush) - tlb_flush_mmu_tlbonly(tlb); + huge_pmd_unshare_flush(tlb, vma); } void __hugetlb_zap_begin(struct vm_area_struct *vma, @@ -6409,11 +6400,11 @@ long hugetlb_change_protection(struct vm_area_struct *vma, pte_t pte; struct hstate *h = hstate_vma(vma); long pages = 0, psize = huge_page_size(h); - bool shared_pmd = false; struct mmu_notifier_range range; unsigned long last_addr_mask; bool uffd_wp = cp_flags & MM_CP_UFFD_WP; bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE; + struct mmu_gather tlb; /* * In the case of shared PMDs, the area to flush could be beyond @@ -6426,6 +6417,7 @@ long hugetlb_change_protection(struct vm_area_struct *vma, BUG_ON(address >= end); flush_cache_range(vma, range.start, range.end); + tlb_gather_mmu_vma(&tlb, vma); mmu_notifier_invalidate_range_start(&range); hugetlb_vma_lock_write(vma); @@ -6452,7 +6444,7 @@ long hugetlb_change_protection(struct vm_area_struct *vma, } } ptl = huge_pte_lock(h, mm, ptep); - if (huge_pmd_unshare(mm, vma, address, ptep)) { + if (huge_pmd_unshare(&tlb, vma, address, ptep)) { /* * When uffd-wp is enabled on the vma, unshare * shouldn't happen at all. Warn about it if it @@ -6461,7 +6453,6 @@ long hugetlb_change_protection(struct vm_area_struct *vma, WARN_ON_ONCE(uffd_wp || uffd_wp_resolve); pages++; spin_unlock(ptl); - shared_pmd = true; address |= last_addr_mask; continue; } @@ -6522,22 +6513,16 @@ long hugetlb_change_protection(struct vm_area_struct *vma, pte = huge_pte_clear_uffd_wp(pte); huge_ptep_modify_prot_commit(vma, address, ptep, old_pte, pte); pages++; + tlb_remove_huge_tlb_entry(h, &tlb, ptep, address); } next: spin_unlock(ptl); cond_resched(); } - /* - * There is nothing protecting a previously-shared page table that we - * unshared through huge_pmd_unshare() from getting freed after we - * release i_mmap_rwsem, so flush the TLB now. If huge_pmd_unshare() - * succeeded, flush the range corresponding to the pud. - */ - if (shared_pmd) - flush_hugetlb_tlb_range(vma, range.start, range.end); - else - flush_hugetlb_tlb_range(vma, start, end); + + tlb_flush_mmu_tlbonly(&tlb); + huge_pmd_unshare_flush(&tlb, vma); /* * No need to call mmu_notifier_arch_invalidate_secondary_tlbs() we are * downgrading page table protection not changing it to point to a new @@ -6548,6 +6533,7 @@ long hugetlb_change_protection(struct vm_area_struct *vma, i_mmap_unlock_write(vma->vm_file->f_mapping); hugetlb_vma_unlock_write(vma); mmu_notifier_invalidate_range_end(&range); + tlb_finish_mmu(&tlb); return pages > 0 ? (pages << h->order) : pages; } @@ -6904,18 +6890,27 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, return pte; } -/* - * unmap huge page backed by shared pte. +/** + * huge_pmd_unshare - Unmap a pmd table if it is shared by multiple users + * @tlb: the current mmu_gather. + * @vma: the vma covering the pmd table. + * @addr: the address we are trying to unshare. + * @ptep: pointer into the (pmd) page table. + * + * Called with the page table lock held, the i_mmap_rwsem held in write mode + * and the hugetlb vma lock held in write mode. * - * Called with page table lock held. + * Note: The caller must call huge_pmd_unshare_flush() before dropping the + * i_mmap_rwsem. * - * returns: 1 successfully unmapped a shared pte page - * 0 the underlying pte page is not shared, or it is the last user + * Returns: 1 if it was a shared PMD table and it got unmapped, or 0 if it + * was not a shared PMD table. */ -int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long addr, pte_t *ptep) +int huge_pmd_unshare(struct mmu_gather *tlb, struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep) { unsigned long sz = huge_page_size(hstate_vma(vma)); + struct mm_struct *mm = vma->vm_mm; pgd_t *pgd = pgd_offset(mm, addr); p4d_t *p4d = p4d_offset(pgd, addr); pud_t *pud = pud_offset(p4d, addr); @@ -6927,18 +6922,36 @@ int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, i_mmap_assert_write_locked(vma->vm_file->f_mapping); hugetlb_vma_assert_locked(vma); pud_clear(pud); - /* - * Once our caller drops the rmap lock, some other process might be - * using this page table as a normal, non-hugetlb page table. - * Wait for pending gup_fast() in other threads to finish before letting - * that happen. - */ - tlb_remove_table_sync_one(); - ptdesc_pmd_pts_dec(virt_to_ptdesc(ptep)); + + tlb_unshare_pmd_ptdesc(tlb, virt_to_ptdesc(ptep), addr); + mm_dec_nr_pmds(mm); return 1; } +/* + * huge_pmd_unshare_flush - Complete a sequence of huge_pmd_unshare() calls + * @tlb: the current mmu_gather. + * @vma: the vma covering the pmd table. + * + * Perform necessary TLB flushes or IPI broadcasts to synchronize PMD table + * unsharing with concurrent page table walkers. + * + * This function must be called after a sequence of huge_pmd_unshare() + * calls while still holding the i_mmap_rwsem. + */ +void huge_pmd_unshare_flush(struct mmu_gather *tlb, struct vm_area_struct *vma) +{ + /* + * We must synchronize page table unsharing such that nobody will + * try reusing a previously-shared page table while it might still + * be in use by previous sharers (TLB, GUP_fast). + */ + i_mmap_assert_write_locked(vma->vm_file->f_mapping); + + tlb_flush_unshared_tables(tlb); +} + #else /* !CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING */ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, @@ -6947,12 +6960,16 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, return NULL; } -int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long addr, pte_t *ptep) +int huge_pmd_unshare(struct mmu_gather *tlb, struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep) { return 0; } +void huge_pmd_unshare_flush(struct mmu_gather *tlb, struct vm_area_struct *vma) +{ +} + void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, unsigned long *start, unsigned long *end) { @@ -7219,6 +7236,7 @@ static void hugetlb_unshare_pmds(struct vm_area_struct *vma, unsigned long sz = huge_page_size(h); struct mm_struct *mm = vma->vm_mm; struct mmu_notifier_range range; + struct mmu_gather tlb; unsigned long address; spinlock_t *ptl; pte_t *ptep; @@ -7230,6 +7248,8 @@ static void hugetlb_unshare_pmds(struct vm_area_struct *vma, return; flush_cache_range(vma, start, end); + tlb_gather_mmu_vma(&tlb, vma); + /* * No need to call adjust_range_if_pmd_sharing_possible(), because * we have already done the PUD_SIZE alignment. @@ -7248,10 +7268,10 @@ static void hugetlb_unshare_pmds(struct vm_area_struct *vma, if (!ptep) continue; ptl = huge_pte_lock(h, mm, ptep); - huge_pmd_unshare(mm, vma, address, ptep); + huge_pmd_unshare(&tlb, vma, address, ptep); spin_unlock(ptl); } - flush_hugetlb_tlb_range(vma, start, end); + huge_pmd_unshare_flush(&tlb, vma); if (take_locks) { i_mmap_unlock_write(vma->vm_file->f_mapping); hugetlb_vma_unlock_write(vma); @@ -7261,6 +7281,7 @@ static void hugetlb_unshare_pmds(struct vm_area_struct *vma, * Documentation/mm/mmu_notifier.rst. */ mmu_notifier_invalidate_range_end(&range); + tlb_finish_mmu(&tlb); } /* diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c index 247e3f9db6c7a..cd32c2dbf501b 100644 --- a/mm/mmu_gather.c +++ b/mm/mmu_gather.c @@ -10,6 +10,7 @@ #include <linux/swap.h> #include <linux/rmap.h> #include <linux/pgalloc.h> +#include <linux/hugetlb.h> #include <asm/tlb.h> @@ -426,6 +427,7 @@ static void __tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, #endif tlb->vma_pfn = 0; + tlb->fully_unshared_tables = 0; __tlb_reset_range(tlb); inc_tlb_flush_pending(tlb->mm); } @@ -459,6 +461,31 @@ void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm) __tlb_gather_mmu(tlb, mm, true); } +/** + * tlb_gather_mmu - initialize an mmu_gather structure for operating on a single + * VMA + * @tlb: the mmu_gather structure to initialize + * @vma: the vm_area_struct + * + * Called to initialize an (on-stack) mmu_gather structure for operating on + * a single VMA. In contrast to tlb_gather_mmu(), calling this function will + * not require another call to tlb_start_vma(). In contrast to tlb_start_vma(), + * this function will *not* call flush_cache_range(). + * + * For hugetlb VMAs, this function will also initialize the mmu_gather + * page_size accordingly, not requiring a separate call to + * tlb_change_page_size(). + * + */ +void tlb_gather_mmu_vma(struct mmu_gather *tlb, struct vm_area_struct *vma) +{ + tlb_gather_mmu(tlb, vma->vm_mm); + tlb_update_vma_flags(tlb, vma); + if (is_vm_hugetlb_page(vma)) + /* All entries have the same size. */ + tlb_change_page_size(tlb, huge_page_size(hstate_vma(vma))); +} + /** * tlb_finish_mmu - finish an mmu_gather structure * @tlb: the mmu_gather structure to finish @@ -468,6 +495,12 @@ void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm) */ void tlb_finish_mmu(struct mmu_gather *tlb) { + /* + * We expect an earlier huge_pmd_unshare_flush() call to sort this out, + * due to complicated locking requirements with page table unsharing. + */ + VM_WARN_ON_ONCE(tlb->fully_unshared_tables); + /* * If there are parallel threads are doing PTE changes on same range * under non-exclusive lock (e.g., mmap_lock read-side) but defer TLB diff --git a/mm/rmap.c b/mm/rmap.c index 748f48727a162..7b9879ef442d9 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -76,7 +76,7 @@ #include <linux/mm_inline.h> #include <linux/oom.h> -#include <asm/tlbflush.h> +#include <asm/tlb.h> #define CREATE_TRACE_POINTS #include <trace/events/migrate.h> @@ -2008,13 +2008,17 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, * if unsuccessful. */ if (!anon) { + struct mmu_gather tlb; + VM_BUG_ON(!(flags & TTU_RMAP_LOCKED)); if (!hugetlb_vma_trylock_write(vma)) goto walk_abort; - if (huge_pmd_unshare(mm, vma, address, pvmw.pte)) { + + tlb_gather_mmu_vma(&tlb, vma); + if (huge_pmd_unshare(&tlb, vma, address, pvmw.pte)) { hugetlb_vma_unlock_write(vma); - flush_tlb_range(vma, - range.start, range.end); + huge_pmd_unshare_flush(&tlb, vma); + tlb_finish_mmu(&tlb); /* * The PMD table was unmapped, * consequently unmapping the folio. @@ -2022,6 +2026,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, goto walk_done; } hugetlb_vma_unlock_write(vma); + tlb_finish_mmu(&tlb); } pteval = huge_ptep_clear_flush(vma, address, pvmw.pte); if (pte_dirty(pteval)) @@ -2398,17 +2403,20 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, * fail if unsuccessful. */ if (!anon) { + struct mmu_gather tlb; + VM_BUG_ON(!(flags & TTU_RMAP_LOCKED)); if (!hugetlb_vma_trylock_write(vma)) { page_vma_mapped_walk_done(&pvmw); ret = false; break; } - if (huge_pmd_unshare(mm, vma, address, pvmw.pte)) { - hugetlb_vma_unlock_write(vma); - flush_tlb_range(vma, - range.start, range.end); + tlb_gather_mmu_vma(&tlb, vma); + if (huge_pmd_unshare(&tlb, vma, address, pvmw.pte)) { + hugetlb_vma_unlock_write(vma); + huge_pmd_unshare_flush(&tlb, vma); + tlb_finish_mmu(&tlb); /* * The PMD table was unmapped, * consequently unmapping the folio. @@ -2417,6 +2425,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, break; } hugetlb_vma_unlock_write(vma); + tlb_finish_mmu(&tlb); } /* Nuke the hugetlb page table entry */ pteval = huge_ptep_clear_flush(vma, address, pvmw.pte); -- 2.52.0

19 hours, 34 minutes

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[PATCH RESEND v3 1/4] mm/hugetlb: fix hugetlb_pmd_shared()

by David Hildenbrand (Red Hat)

We switched from (wrongly) using the page count to an independent shared count. Now, shared page tables have a refcount of 1 (excluding speculative references) and instead use ptdesc->pt_share_count to identify sharing. We didn't convert hugetlb_pmd_shared(), so right now, we would never detect a shared PMD table as such, because sharing/unsharing no longer touches the refcount of a PMD table. Page migration, like mbind() or migrate_pages() would allow for migrating folios mapped into such shared PMD tables, even though the folios are not exclusive. In smaps we would account them as "private" although they are "shared", and we would be wrongly setting the PM_MMAP_EXCLUSIVE in the pagemap interface. Fix it by properly using ptdesc_pmd_is_shared() in hugetlb_pmd_shared(). Fixes: 59d9094df3d7 ("mm: hugetlb: independent PMD page table shared count") Reviewed-by: Rik van Riel <riel(a)surriel.com> Reviewed-by: Lance Yang <lance.yang(a)linux.dev> Tested-by: Lance Yang <lance.yang(a)linux.dev> Reviewed-by: Harry Yoo <harry.yoo(a)oracle.com> Tested-by: Laurence Oberman <loberman(a)redhat.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes(a)oracle.com> Acked-by: Oscar Salvador <osalvador(a)suse.de> Cc: <stable(a)vger.kernel.org> Cc: Liu Shixin <liushixin2(a)huawei.com> Signed-off-by: David Hildenbrand (Red Hat) <david(a)kernel.org> --- include/linux/hugetlb.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 019a1c5281e4e..03c8725efa289 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -1326,7 +1326,7 @@ static inline __init void hugetlb_cma_reserve(int order) #ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING static inline bool hugetlb_pmd_shared(pte_t *pte) { - return page_count(virt_to_page(pte)) > 1; + return ptdesc_pmd_is_shared(virt_to_ptdesc(pte)); } #else static inline bool hugetlb_pmd_shared(pte_t *pte) -- 2.52.0

19 hours, 34 minutes

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[PATCH v3 3/3] mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather

by David Hildenbrand (Red Hat)

As reported, ever since commit 1013af4f585f ("mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race") we can end up in some situations where we perform so many IPI broadcasts when unsharing hugetlb PMD page tables that it severely regresses some workloads. In particular, when we fork()+exit(), or when we munmap() a large area backed by many shared PMD tables, we perform one IPI broadcast per unshared PMD table. There are two optimizations to be had: (1) When we process (unshare) multiple such PMD tables, such as during exit(), it is sufficient to send a single IPI broadcast (as long as we respect locking rules) instead of one per PMD table. Locking prevents that any of these PMD tables could get reused before we drop the lock. (2) When we are not the last sharer (> 2 users including us), there is no need to send the IPI broadcast. The shared PMD tables cannot become exclusive (fully unshared) before an IPI will be broadcasted by the last sharer. Concurrent GUP-fast could walk into a PMD table just before we unshared it. It could then succeed in grabbing a page from the shared page table even after munmap() etc succeeded (and supressed an IPI). But there is not difference compared to GUP-fast just sleeping for a while after grabbing the page and re-enabling IRQs. Most importantly, GUP-fast will never walk into page tables that are no-longer shared, because the last sharer will issue an IPI broadcast. (if ever required, checking whether the PUD changed in GUP-fast after grabbing the page like we do in the PTE case could handle this) So let's rework PMD sharing TLB flushing + IPI sync to use the mmu_gather infrastructure so we can implement these optimizations and demystify the code at least a bit. Extend the mmu_gather infrastructure to be able to deal with our special hugetlb PMD table sharing implementation. To make initialization of the mmu_gather easier when working on a single VMA (in particular, when dealing with hugetlb), provide tlb_gather_mmu_vma(). We'll consolidate the handling for (full) unsharing of PMD tables in tlb_unshare_pmd_ptdesc() and tlb_flush_unshared_tables(), and track in "struct mmu_gather" whether we had (full) unsharing of PMD tables. Because locking is very special (concurrent unsharing+reuse must be prevented), we disallow deferring flushing to tlb_finish_mmu() and instead require an explicit earlier call to tlb_flush_unshared_tables(). From hugetlb code, we call huge_pmd_unshare_flush() where we make sure that the expected lock protecting us from concurrent unsharing+reuse is still held. Check with a VM_WARN_ON_ONCE() in tlb_finish_mmu() that tlb_flush_unshared_tables() was properly called earlier. Document it all properly. Notes about tlb_remove_table_sync_one() interaction with unsharing: There are two fairly tricky things: (1) tlb_remove_table_sync_one() is a NOP on architectures without CONFIG_MMU_GATHER_RCU_TABLE_FREE. Here, the assumption is that the previous TLB flush would send an IPI to all relevant CPUs. Careful: some architectures like x86 only send IPIs to all relevant CPUs when tlb->freed_tables is set. The relevant architectures should be selecting MMU_GATHER_RCU_TABLE_FREE, but x86 might not do that in stable kernels and it might have been problematic before this patch. Also, the arch flushing behavior (independent of IPIs) is different when tlb->freed_tables is set. Do we have to enlighten them to also take care of tlb->unshared_tables? So far we didn't care, so hopefully we are fine. Of course, we could be setting tlb->freed_tables as well, but that might then unnecessarily flush too much, because the semantics of tlb->freed_tables are a bit fuzzy. This patch changes nothing in this regard. (2) tlb_remove_table_sync_one() is not a NOP on architectures with CONFIG_MMU_GATHER_RCU_TABLE_FREE that actually don't need a sync. Take x86 as an example: in the common case (!pv, !X86_FEATURE_INVLPGB) we still issue IPIs during TLB flushes and don't actually need the second tlb_remove_table_sync_one(). This optimized can be implemented on top of this, by checking e.g., in tlb_remove_table_sync_one() whether we really need IPIs. But as described in (1), it really must honor tlb->freed_tables then to send IPIs to all relevant CPUs. Notes on TLB flushing changes: (1) Flushing for non-shared PMD tables We're converting from flush_hugetlb_tlb_range() to tlb_remove_huge_tlb_entry(). Given that we properly initialize the MMU gather in tlb_gather_mmu_vma() to be hugetlb aware, similar to __unmap_hugepage_range(), that should be fine. (2) Flushing for shared PMD tables We're converting from various things (flush_hugetlb_tlb_range(), tlb_flush_pmd_range(), flush_tlb_range()) to tlb_flush_pmd_range(). tlb_flush_pmd_range() achieves the same that tlb_remove_huge_tlb_entry() would achieve in these scenarios. Note that tlb_remove_huge_tlb_entry() also calls __tlb_remove_tlb_entry(), however that is only implemented on powerpc, which does not support PMD table sharing. Similar to (1), tlb_gather_mmu_vma() should make sure that TLB flushing keeps on working as expected. Further, note that the ptdesc_pmd_pts_dec() in huge_pmd_share() is not a concern, as we are holding the i_mmap_lock the whole time, preventing concurrent unsharing. That ptdesc_pmd_pts_dec() usage will be removed separately as a cleanup later. There are plenty more cleanups to be had, but they have to wait until this is fixed. Fixes: 1013af4f585f ("mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race") Reported-by: Uschakow, Stanislav" <suschako(a)amazon.de> Closes: https://lore.kernel.org/all/4d3878531c76479d9f8ca9789dc6485d@amazon.de/ Tested-by: Laurence Oberman <loberman(a)redhat.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: David Hildenbrand (Red Hat) <david(a)kernel.org> --- include/asm-generic/tlb.h | 77 +++++++++++++++++++++++- include/linux/hugetlb.h | 15 +++-- include/linux/mm_types.h | 1 + mm/hugetlb.c | 123 ++++++++++++++++++++++---------------- mm/mmu_gather.c | 33 ++++++++++ mm/rmap.c | 25 +++++--- 6 files changed, 208 insertions(+), 66 deletions(-) diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h index 1fff717cae510..4d679d2a206b4 100644 --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -46,7 +46,8 @@ * * The mmu_gather API consists of: * - * - tlb_gather_mmu() / tlb_gather_mmu_fullmm() / tlb_finish_mmu() + * - tlb_gather_mmu() / tlb_gather_mmu_fullmm() / tlb_gather_mmu_vma() / + * tlb_finish_mmu() * * start and finish a mmu_gather * @@ -364,6 +365,20 @@ struct mmu_gather { unsigned int vma_huge : 1; unsigned int vma_pfn : 1; + /* + * Did we unshare (unmap) any shared page tables? For now only + * used for hugetlb PMD table sharing. + */ + unsigned int unshared_tables : 1; + + /* + * Did we unshare any page tables such that they are now exclusive + * and could get reused+modified by the new owner? When setting this + * flag, "unshared_tables" will be set as well. For now only used + * for hugetlb PMD table sharing. + */ + unsigned int fully_unshared_tables : 1; + unsigned int batch_count; #ifndef CONFIG_MMU_GATHER_NO_GATHER @@ -400,6 +415,7 @@ static inline void __tlb_reset_range(struct mmu_gather *tlb) tlb->cleared_pmds = 0; tlb->cleared_puds = 0; tlb->cleared_p4ds = 0; + tlb->unshared_tables = 0; /* * Do not reset mmu_gather::vma_* fields here, we do not * call into tlb_start_vma() again to set them if there is an @@ -484,7 +500,7 @@ static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb) * these bits. */ if (!(tlb->freed_tables || tlb->cleared_ptes || tlb->cleared_pmds || - tlb->cleared_puds || tlb->cleared_p4ds)) + tlb->cleared_puds || tlb->cleared_p4ds || tlb->unshared_tables)) return; tlb_flush(tlb); @@ -773,6 +789,63 @@ static inline bool huge_pmd_needs_flush(pmd_t oldpmd, pmd_t newpmd) } #endif +#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING +static inline void tlb_unshare_pmd_ptdesc(struct mmu_gather *tlb, struct ptdesc *pt, + unsigned long addr) +{ + /* + * The caller must make sure that concurrent unsharing + exclusive + * reuse is impossible until tlb_flush_unshared_tables() was called. + */ + VM_WARN_ON_ONCE(!ptdesc_pmd_is_shared(pt)); + ptdesc_pmd_pts_dec(pt); + + /* Clearing a PUD pointing at a PMD table with PMD leaves. */ + tlb_flush_pmd_range(tlb, addr & PUD_MASK, PUD_SIZE); + + /* + * If the page table is now exclusively owned, we fully unshared + * a page table. + */ + if (!ptdesc_pmd_is_shared(pt)) + tlb->fully_unshared_tables = true; + tlb->unshared_tables = true; +} + +static inline void tlb_flush_unshared_tables(struct mmu_gather *tlb) +{ + /* + * As soon as the caller drops locks to allow for reuse of + * previously-shared tables, these tables could get modified and + * even reused outside of hugetlb context, so we have to make sure that + * any page table walkers (incl. TLB, GUP-fast) are aware of that + * change. + * + * Even if we are not fully unsharing a PMD table, we must + * flush the TLB for the unsharer now. + */ + if (tlb->unshared_tables) + tlb_flush_mmu_tlbonly(tlb); + + /* + * Similarly, we must make sure that concurrent GUP-fast will not + * walk previously-shared page tables that are getting modified+reused + * elsewhere. So broadcast an IPI to wait for any concurrent GUP-fast. + * + * We only perform this when we are the last sharer of a page table, + * as the IPI will reach all CPUs: any GUP-fast. + * + * Note that on configs where tlb_remove_table_sync_one() is a NOP, + * the expectation is that the tlb_flush_mmu_tlbonly() would have issued + * required IPIs already for us. + */ + if (tlb->fully_unshared_tables) { + tlb_remove_table_sync_one(); + tlb->fully_unshared_tables = false; + } +} +#endif /* CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING */ + #endif /* CONFIG_MMU */ #endif /* _ASM_GENERIC__TLB_H */ diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 03c8725efa289..e51b8ef0cebd9 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -240,8 +240,9 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma, pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr, unsigned long sz); unsigned long hugetlb_mask_last_page(struct hstate *h); -int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long addr, pte_t *ptep); +int huge_pmd_unshare(struct mmu_gather *tlb, struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep); +void huge_pmd_unshare_flush(struct mmu_gather *tlb, struct vm_area_struct *vma); void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, unsigned long *start, unsigned long *end); @@ -300,13 +301,17 @@ static inline struct address_space *hugetlb_folio_mapping_lock_write( return NULL; } -static inline int huge_pmd_unshare(struct mm_struct *mm, - struct vm_area_struct *vma, - unsigned long addr, pte_t *ptep) +static inline int huge_pmd_unshare(struct mmu_gather *tlb, + struct vm_area_struct *vma, unsigned long addr, pte_t *ptep) { return 0; } +static inline void huge_pmd_unshare_flush(struct mmu_gather *tlb, + struct vm_area_struct *vma) +{ +} + static inline void adjust_range_if_pmd_sharing_possible( struct vm_area_struct *vma, unsigned long *start, unsigned long *end) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 42af2292951d4..d1053b2c1f800 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1522,6 +1522,7 @@ static inline unsigned int mm_cid_size(void) struct mmu_gather; extern void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm); extern void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm); +void tlb_gather_mmu_vma(struct mmu_gather *tlb, struct vm_area_struct *vma); extern void tlb_finish_mmu(struct mmu_gather *tlb); struct vm_fault; diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 3c77cdef12a32..2609b6d58f99e 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5096,7 +5096,7 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, unsigned long last_addr_mask; pte_t *src_pte, *dst_pte; struct mmu_notifier_range range; - bool shared_pmd = false; + struct mmu_gather tlb; mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, old_addr, old_end); @@ -5106,6 +5106,7 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, * range. */ flush_cache_range(vma, range.start, range.end); + tlb_gather_mmu_vma(&tlb, vma); mmu_notifier_invalidate_range_start(&range); last_addr_mask = hugetlb_mask_last_page(h); @@ -5122,8 +5123,7 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, if (huge_pte_none(huge_ptep_get(mm, old_addr, src_pte))) continue; - if (huge_pmd_unshare(mm, vma, old_addr, src_pte)) { - shared_pmd = true; + if (huge_pmd_unshare(&tlb, vma, old_addr, src_pte)) { old_addr |= last_addr_mask; new_addr |= last_addr_mask; continue; @@ -5134,15 +5134,16 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, break; move_huge_pte(vma, old_addr, new_addr, src_pte, dst_pte, sz); + tlb_remove_huge_tlb_entry(h, &tlb, src_pte, old_addr); } - if (shared_pmd) - flush_hugetlb_tlb_range(vma, range.start, range.end); - else - flush_hugetlb_tlb_range(vma, old_end - len, old_end); + tlb_flush_mmu_tlbonly(&tlb); + huge_pmd_unshare_flush(&tlb, vma); + mmu_notifier_invalidate_range_end(&range); i_mmap_unlock_write(mapping); hugetlb_vma_unlock_write(vma); + tlb_finish_mmu(&tlb); return len + old_addr - old_end; } @@ -5161,7 +5162,6 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, unsigned long sz = huge_page_size(h); bool adjust_reservation; unsigned long last_addr_mask; - bool force_flush = false; WARN_ON(!is_vm_hugetlb_page(vma)); BUG_ON(start & ~huge_page_mask(h)); @@ -5184,10 +5184,8 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, } ptl = huge_pte_lock(h, mm, ptep); - if (huge_pmd_unshare(mm, vma, address, ptep)) { + if (huge_pmd_unshare(tlb, vma, address, ptep)) { spin_unlock(ptl); - tlb_flush_pmd_range(tlb, address & PUD_MASK, PUD_SIZE); - force_flush = true; address |= last_addr_mask; continue; } @@ -5303,14 +5301,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, } tlb_end_vma(tlb, vma); - /* - * There is nothing protecting a previously-shared page table that we - * unshared through huge_pmd_unshare() from getting freed after we - * release i_mmap_rwsem, so flush the TLB now. If huge_pmd_unshare() - * succeeded, flush the range corresponding to the pud. - */ - if (force_flush) - tlb_flush_mmu_tlbonly(tlb); + huge_pmd_unshare_flush(tlb, vma); } void __hugetlb_zap_begin(struct vm_area_struct *vma, @@ -6409,11 +6400,11 @@ long hugetlb_change_protection(struct vm_area_struct *vma, pte_t pte; struct hstate *h = hstate_vma(vma); long pages = 0, psize = huge_page_size(h); - bool shared_pmd = false; struct mmu_notifier_range range; unsigned long last_addr_mask; bool uffd_wp = cp_flags & MM_CP_UFFD_WP; bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE; + struct mmu_gather tlb; /* * In the case of shared PMDs, the area to flush could be beyond @@ -6426,6 +6417,7 @@ long hugetlb_change_protection(struct vm_area_struct *vma, BUG_ON(address >= end); flush_cache_range(vma, range.start, range.end); + tlb_gather_mmu_vma(&tlb, vma); mmu_notifier_invalidate_range_start(&range); hugetlb_vma_lock_write(vma); @@ -6452,7 +6444,7 @@ long hugetlb_change_protection(struct vm_area_struct *vma, } } ptl = huge_pte_lock(h, mm, ptep); - if (huge_pmd_unshare(mm, vma, address, ptep)) { + if (huge_pmd_unshare(&tlb, vma, address, ptep)) { /* * When uffd-wp is enabled on the vma, unshare * shouldn't happen at all. Warn about it if it @@ -6461,7 +6453,6 @@ long hugetlb_change_protection(struct vm_area_struct *vma, WARN_ON_ONCE(uffd_wp || uffd_wp_resolve); pages++; spin_unlock(ptl); - shared_pmd = true; address |= last_addr_mask; continue; } @@ -6522,22 +6513,16 @@ long hugetlb_change_protection(struct vm_area_struct *vma, pte = huge_pte_clear_uffd_wp(pte); huge_ptep_modify_prot_commit(vma, address, ptep, old_pte, pte); pages++; + tlb_remove_huge_tlb_entry(h, &tlb, ptep, address); } next: spin_unlock(ptl); cond_resched(); } - /* - * There is nothing protecting a previously-shared page table that we - * unshared through huge_pmd_unshare() from getting freed after we - * release i_mmap_rwsem, so flush the TLB now. If huge_pmd_unshare() - * succeeded, flush the range corresponding to the pud. - */ - if (shared_pmd) - flush_hugetlb_tlb_range(vma, range.start, range.end); - else - flush_hugetlb_tlb_range(vma, start, end); + + tlb_flush_mmu_tlbonly(&tlb); + huge_pmd_unshare_flush(&tlb, vma); /* * No need to call mmu_notifier_arch_invalidate_secondary_tlbs() we are * downgrading page table protection not changing it to point to a new @@ -6548,6 +6533,7 @@ long hugetlb_change_protection(struct vm_area_struct *vma, i_mmap_unlock_write(vma->vm_file->f_mapping); hugetlb_vma_unlock_write(vma); mmu_notifier_invalidate_range_end(&range); + tlb_finish_mmu(&tlb); return pages > 0 ? (pages << h->order) : pages; } @@ -6904,18 +6890,27 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, return pte; } -/* - * unmap huge page backed by shared pte. +/** + * huge_pmd_unshare - Unmap a pmd table if it is shared by multiple users + * @tlb: the current mmu_gather. + * @vma: the vma covering the pmd table. + * @addr: the address we are trying to unshare. + * @ptep: pointer into the (pmd) page table. + * + * Called with the page table lock held, the i_mmap_rwsem held in write mode + * and the hugetlb vma lock held in write mode. * - * Called with page table lock held. + * Note: The caller must call huge_pmd_unshare_flush() before dropping the + * i_mmap_rwsem. * - * returns: 1 successfully unmapped a shared pte page - * 0 the underlying pte page is not shared, or it is the last user + * Returns: 1 if it was a shared PMD table and it got unmapped, or 0 if it + * was not a shared PMD table. */ -int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long addr, pte_t *ptep) +int huge_pmd_unshare(struct mmu_gather *tlb, struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep) { unsigned long sz = huge_page_size(hstate_vma(vma)); + struct mm_struct *mm = vma->vm_mm; pgd_t *pgd = pgd_offset(mm, addr); p4d_t *p4d = p4d_offset(pgd, addr); pud_t *pud = pud_offset(p4d, addr); @@ -6927,18 +6922,36 @@ int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, i_mmap_assert_write_locked(vma->vm_file->f_mapping); hugetlb_vma_assert_locked(vma); pud_clear(pud); - /* - * Once our caller drops the rmap lock, some other process might be - * using this page table as a normal, non-hugetlb page table. - * Wait for pending gup_fast() in other threads to finish before letting - * that happen. - */ - tlb_remove_table_sync_one(); - ptdesc_pmd_pts_dec(virt_to_ptdesc(ptep)); + + tlb_unshare_pmd_ptdesc(tlb, virt_to_ptdesc(ptep), addr); + mm_dec_nr_pmds(mm); return 1; } +/* + * huge_pmd_unshare_flush - Complete a sequence of huge_pmd_unshare() calls + * @tlb: the current mmu_gather. + * @vma: the vma covering the pmd table. + * + * Perform necessary TLB flushes or IPI broadcasts to synchronize PMD table + * unsharing with concurrent page table walkers. + * + * This function must be called after a sequence of huge_pmd_unshare() + * calls while still holding the i_mmap_rwsem. + */ +void huge_pmd_unshare_flush(struct mmu_gather *tlb, struct vm_area_struct *vma) +{ + /* + * We must synchronize page table unsharing such that nobody will + * try reusing a previously-shared page table while it might still + * be in use by previous sharers (TLB, GUP_fast). + */ + i_mmap_assert_write_locked(vma->vm_file->f_mapping); + + tlb_flush_unshared_tables(tlb); +} + #else /* !CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING */ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, @@ -6947,12 +6960,16 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, return NULL; } -int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long addr, pte_t *ptep) +int huge_pmd_unshare(struct mmu_gather *tlb, struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep) { return 0; } +void huge_pmd_unshare_flush(struct mmu_gather *tlb, struct vm_area_struct *vma) +{ +} + void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, unsigned long *start, unsigned long *end) { @@ -7219,6 +7236,7 @@ static void hugetlb_unshare_pmds(struct vm_area_struct *vma, unsigned long sz = huge_page_size(h); struct mm_struct *mm = vma->vm_mm; struct mmu_notifier_range range; + struct mmu_gather tlb; unsigned long address; spinlock_t *ptl; pte_t *ptep; @@ -7230,6 +7248,8 @@ static void hugetlb_unshare_pmds(struct vm_area_struct *vma, return; flush_cache_range(vma, start, end); + tlb_gather_mmu_vma(&tlb, vma); + /* * No need to call adjust_range_if_pmd_sharing_possible(), because * we have already done the PUD_SIZE alignment. @@ -7248,10 +7268,10 @@ static void hugetlb_unshare_pmds(struct vm_area_struct *vma, if (!ptep) continue; ptl = huge_pte_lock(h, mm, ptep); - huge_pmd_unshare(mm, vma, address, ptep); + huge_pmd_unshare(&tlb, vma, address, ptep); spin_unlock(ptl); } - flush_hugetlb_tlb_range(vma, start, end); + huge_pmd_unshare_flush(&tlb, vma); if (take_locks) { i_mmap_unlock_write(vma->vm_file->f_mapping); hugetlb_vma_unlock_write(vma); @@ -7261,6 +7281,7 @@ static void hugetlb_unshare_pmds(struct vm_area_struct *vma, * Documentation/mm/mmu_notifier.rst. */ mmu_notifier_invalidate_range_end(&range); + tlb_finish_mmu(&tlb); } /* diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c index 247e3f9db6c7a..cd32c2dbf501b 100644 --- a/mm/mmu_gather.c +++ b/mm/mmu_gather.c @@ -10,6 +10,7 @@ #include <linux/swap.h> #include <linux/rmap.h> #include <linux/pgalloc.h> +#include <linux/hugetlb.h> #include <asm/tlb.h> @@ -426,6 +427,7 @@ static void __tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, #endif tlb->vma_pfn = 0; + tlb->fully_unshared_tables = 0; __tlb_reset_range(tlb); inc_tlb_flush_pending(tlb->mm); } @@ -459,6 +461,31 @@ void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm) __tlb_gather_mmu(tlb, mm, true); } +/** + * tlb_gather_mmu - initialize an mmu_gather structure for operating on a single + * VMA + * @tlb: the mmu_gather structure to initialize + * @vma: the vm_area_struct + * + * Called to initialize an (on-stack) mmu_gather structure for operating on + * a single VMA. In contrast to tlb_gather_mmu(), calling this function will + * not require another call to tlb_start_vma(). In contrast to tlb_start_vma(), + * this function will *not* call flush_cache_range(). + * + * For hugetlb VMAs, this function will also initialize the mmu_gather + * page_size accordingly, not requiring a separate call to + * tlb_change_page_size(). + * + */ +void tlb_gather_mmu_vma(struct mmu_gather *tlb, struct vm_area_struct *vma) +{ + tlb_gather_mmu(tlb, vma->vm_mm); + tlb_update_vma_flags(tlb, vma); + if (is_vm_hugetlb_page(vma)) + /* All entries have the same size. */ + tlb_change_page_size(tlb, huge_page_size(hstate_vma(vma))); +} + /** * tlb_finish_mmu - finish an mmu_gather structure * @tlb: the mmu_gather structure to finish @@ -468,6 +495,12 @@ void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm) */ void tlb_finish_mmu(struct mmu_gather *tlb) { + /* + * We expect an earlier huge_pmd_unshare_flush() call to sort this out, + * due to complicated locking requirements with page table unsharing. + */ + VM_WARN_ON_ONCE(tlb->fully_unshared_tables); + /* * If there are parallel threads are doing PTE changes on same range * under non-exclusive lock (e.g., mmap_lock read-side) but defer TLB diff --git a/mm/rmap.c b/mm/rmap.c index 748f48727a162..7b9879ef442d9 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -76,7 +76,7 @@ #include <linux/mm_inline.h> #include <linux/oom.h> -#include <asm/tlbflush.h> +#include <asm/tlb.h> #define CREATE_TRACE_POINTS #include <trace/events/migrate.h> @@ -2008,13 +2008,17 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, * if unsuccessful. */ if (!anon) { + struct mmu_gather tlb; + VM_BUG_ON(!(flags & TTU_RMAP_LOCKED)); if (!hugetlb_vma_trylock_write(vma)) goto walk_abort; - if (huge_pmd_unshare(mm, vma, address, pvmw.pte)) { + + tlb_gather_mmu_vma(&tlb, vma); + if (huge_pmd_unshare(&tlb, vma, address, pvmw.pte)) { hugetlb_vma_unlock_write(vma); - flush_tlb_range(vma, - range.start, range.end); + huge_pmd_unshare_flush(&tlb, vma); + tlb_finish_mmu(&tlb); /* * The PMD table was unmapped, * consequently unmapping the folio. @@ -2022,6 +2026,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, goto walk_done; } hugetlb_vma_unlock_write(vma); + tlb_finish_mmu(&tlb); } pteval = huge_ptep_clear_flush(vma, address, pvmw.pte); if (pte_dirty(pteval)) @@ -2398,17 +2403,20 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, * fail if unsuccessful. */ if (!anon) { + struct mmu_gather tlb; + VM_BUG_ON(!(flags & TTU_RMAP_LOCKED)); if (!hugetlb_vma_trylock_write(vma)) { page_vma_mapped_walk_done(&pvmw); ret = false; break; } - if (huge_pmd_unshare(mm, vma, address, pvmw.pte)) { - hugetlb_vma_unlock_write(vma); - flush_tlb_range(vma, - range.start, range.end); + tlb_gather_mmu_vma(&tlb, vma); + if (huge_pmd_unshare(&tlb, vma, address, pvmw.pte)) { + hugetlb_vma_unlock_write(vma); + huge_pmd_unshare_flush(&tlb, vma); + tlb_finish_mmu(&tlb); /* * The PMD table was unmapped, * consequently unmapping the folio. @@ -2417,6 +2425,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, break; } hugetlb_vma_unlock_write(vma); + tlb_finish_mmu(&tlb); } /* Nuke the hugetlb page table entry */ pteval = huge_ptep_clear_flush(vma, address, pvmw.pte); -- 2.52.0

20 hours, 23 minutes

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[PATCH 1/2] ublk: add UBLK_F_NO_AUTO_PART_SCAN feature flag

by Ming Lei

Add a new feature flag UBLK_F_NO_AUTO_PART_SCAN to allow users to suppress automatic partition scanning when starting a ublk device. This is useful for network-backed devices where partition scanning can cause issues: - Partition scan triggers synchronous I/O during device startup - If userspace server crashes during scan, recovery is problematic - For remotely-managed devices, partition probing may not be needed Users can manually trigger partition scanning later when appropriate using standard tools (e.g., partprobe, blockdev --rereadpt). Reported-by: Yoav Cohen <yoav(a)nvidia.com> Link: https://lore.kernel.org/linux-block/DM4PR12MB63280C5637917C071C2F0D65A9A8A@… Cc: stable(a)vger.kernel.org Signed-off-by: Ming Lei <ming.lei(a)redhat.com> --- - suggest to backport to stable, which is useful for avoiding problematic recovery, also the change is simple enough drivers/block/ublk_drv.c | 16 +++++++++++++--- include/uapi/linux/ublk_cmd.h | 8 ++++++++ 2 files changed, 21 insertions(+), 3 deletions(-) diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c index 78f3e22151b9..ca6ec8ed443f 100644 --- a/drivers/block/ublk_drv.c +++ b/drivers/block/ublk_drv.c @@ -73,7 +73,8 @@ | UBLK_F_AUTO_BUF_REG \ | UBLK_F_QUIESCE \ | UBLK_F_PER_IO_DAEMON \ - | UBLK_F_BUF_REG_OFF_DAEMON) + | UBLK_F_BUF_REG_OFF_DAEMON \ + | UBLK_F_NO_AUTO_PART_SCAN) #define UBLK_F_ALL_RECOVERY_FLAGS (UBLK_F_USER_RECOVERY \ | UBLK_F_USER_RECOVERY_REISSUE \ @@ -2930,8 +2931,13 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub, ublk_apply_params(ub); - /* don't probe partitions if any daemon task is un-trusted */ - if (ub->unprivileged_daemons) + /* + * Don't probe partitions if: + * - any daemon task is un-trusted, or + * - user explicitly requested to suppress partition scan + */ + if (ub->unprivileged_daemons || + (ub->dev_info.flags & UBLK_F_NO_AUTO_PART_SCAN)) set_bit(GD_SUPPRESS_PART_SCAN, &disk->state); ublk_get_device(ub); @@ -2947,6 +2953,10 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub, if (ret) goto out_put_cdev; + /* allow user to probe partitions from userspace */ + if (!ub->unprivileged_daemons && + (ub->dev_info.flags & UBLK_F_NO_AUTO_PART_SCAN)) + clear_bit(GD_SUPPRESS_PART_SCAN, &disk->state); set_bit(UB_STATE_USED, &ub->state); out_put_cdev: diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h index ec77dabba45b..0827db14a215 100644 --- a/include/uapi/linux/ublk_cmd.h +++ b/include/uapi/linux/ublk_cmd.h @@ -311,6 +311,14 @@ */ #define UBLK_F_BUF_REG_OFF_DAEMON (1ULL << 14) +/* + * If this feature is set, the kernel will not automatically scan for partitions + * when the device is started. This is useful for network-backed devices where + * partition scanning can cause deadlocks if the userspace server crashes during + * the scan. Users can manually trigger partition scanning later when appropriate. + */ +#define UBLK_F_NO_AUTO_PART_SCAN (1ULL << 15) + /* device state */ #define UBLK_S_DEV_DEAD 0 #define UBLK_S_DEV_LIVE 1 -- 2.47.0

21 hours, 11 minutes

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[alternative-merged] buildid-validate-page-backed-file-before-parsing-build-id.patch removed from -mm tree

by Andrew Morton

The quilt patch titled Subject: buildid: validate page-backed file before parsing build ID has been removed from the -mm tree. Its filename was buildid-validate-page-backed-file-before-parsing-build-id.patch This patch was dropped because an alternative patch was or shall be merged ------------------------------------------------------ From: Jinchao Wang <wangjinchao600(a)gmail.com> Subject: buildid: validate page-backed file before parsing build ID Date: Tue, 23 Dec 2025 18:32:07 +0800 __build_id_parse() only works on page-backed storage. Its helper paths eventually call mapping->a_ops->read_folio(), so explicitly reject VMAs that do not map a regular file or lack valid address_space operations. Link: https://lkml.kernel.org/r/20251223103214.2412446-1-wangjinchao600@gmail.com Fixes: ad41251c290d ("lib/buildid: implement sleepable build_id_parse() API") Signed-off-by: Jinchao Wang <wangjinchao600(a)gmail.com> Reported-by: <syzbot+e008db2ac01e282550ee(a)syzkaller.appspotmail.com> Tested-by: <syzbot+e008db2ac01e282550ee(a)syzkaller.appspotmail.com> Link: https://lkml.kernel.org/r/694a67ab.050a0220.19928e.001c.GAE@google.com Closes: https://lkml.kernel.org/r/693540fe.a70a0220.38f243.004c.GAE@google.com Cc: Axel Rasmussen <axelrasmussen(a)google.com> Cc: David Hildenbrand (Red Hat) <david(a)kernel.org> Cc: Johannes Weiner <hannes(a)cmpxchg.org> Cc: Lorenzo Stoakes <lorenzo.stoakes(a)oracle.com> Cc: Michal Hocko <mhocko(a)kernel.org> Cc: Qi Zheng <zhengqi.arch(a)bytedance.com> Cc: Shakeel Butt <shakeel.butt(a)linux.dev> Cc: Wei Xu <weixugc(a)google.com> Cc: Yuanchu Xie <yuanchu(a)google.com> Cc: Andrii Nakryiko <andrii(a)kernel.org> Cc: Eduard Zingerman <eddyz87(a)gmail.com> Cc: Omar Sandoval <osandov(a)fb.com> Cc: Deepanshu Kartikey <kartikey406(a)gmail.com> Cc: Alexei Starovoitov <ast(a)kernel.org> Cc: Daniel Borkman <daniel(a)iogearbox.net> Cc: Hao Luo <haoluo(a)google.com> Cc: Jiri Olsa <jolsa(a)kernel.org> Cc: John Fastabend <john.fastabend(a)gmail.com> Cc: KP Singh <kpsingh(a)kernel.org> Cc: Martin KaFai Lau <martin.lau(a)linux.dev> Cc: Song Liu <song(a)kernel.org> Cc: Stanislav Fomichev <sdf(a)fomichev.me> Cc: Yonghong Song <yonghong.song(a)linux.dev> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- lib/buildid.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/lib/buildid.c~buildid-validate-page-backed-file-before-parsing-build-id +++ a/lib/buildid.c @@ -288,7 +288,10 @@ static int __build_id_parse(struct vm_ar int ret; /* only works for page backed storage */ - if (!vma->vm_file) + if (!vma->vm_file || + !S_ISREG(file_inode(vma->vm_file)->i_mode) || + !vma->vm_file->f_mapping->a_ops || + !vma->vm_file->f_mapping->a_ops->read_folio) return -EINVAL; freader_init_from_file(&r, buf, sizeof(buf), vma->vm_file, may_fault); _ Patches currently in -mm which might be from wangjinchao600(a)gmail.com are

21 hours, 47 minutes

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[merged mm-hotfixes-stable] mm-page_owner-fix-memory-leak-in-page_owner_stack_fops-release.patch removed from -mm tree

by Andrew Morton

The quilt patch titled Subject: mm/page_owner: fix memory leak in page_owner_stack_fops->release() has been removed from the -mm tree. Its filename was mm-page_owner-fix-memory-leak-in-page_owner_stack_fops-release.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Ran Xiaokai <ran.xiaokai(a)zte.com.cn> Subject: mm/page_owner: fix memory leak in page_owner_stack_fops->release() Date: Fri, 19 Dec 2025 07:42:32 +0000 The page_owner_stack_fops->open() callback invokes seq_open_private(), therefore its corresponding ->release() callback must call seq_release_private(). Otherwise it will cause a memory leak of struct stack_print_ctx. Link: https://lkml.kernel.org/r/20251219074232.136482-1-ranxiaokai627@163.com Fixes: 765973a09803 ("mm,page_owner: display all stacks and their count") Signed-off-by: Ran Xiaokai <ran.xiaokai(a)zte.com.cn> Acked-by: Michal Hocko <mhocko(a)suse.com> Acked-by: Vlastimil Babka <vbabka(a)suse.cz> Cc: Andrey Konovalov <andreyknvl(a)gmail.com> Cc: Brendan Jackman <jackmanb(a)google.com> Cc: Johannes Weiner <hannes(a)cmpxchg.org> Cc: Marco Elver <elver(a)google.com> Cc: Suren Baghdasaryan <surenb(a)google.com> Cc: Zi Yan <ziy(a)nvidia.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- mm/page_owner.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/page_owner.c~mm-page_owner-fix-memory-leak-in-page_owner_stack_fops-release +++ a/mm/page_owner.c @@ -952,7 +952,7 @@ static const struct file_operations page .open = page_owner_stack_open, .read = seq_read, .llseek = seq_lseek, - .release = seq_release, + .release = seq_release_private, }; static int page_owner_threshold_get(void *data, u64 *val) _ Patches currently in -mm which might be from ran.xiaokai(a)zte.com.cn are

21 hours, 50 minutes

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[merged mm-hotfixes-stable] mm-consider-non-anon-swap-cache-folios-in-folio_expected_ref_count.patch removed from -mm tree

by Andrew Morton

The quilt patch titled Subject: mm: consider non-anon swap cache folios in folio_expected_ref_count() has been removed from the -mm tree. Its filename was mm-consider-non-anon-swap-cache-folios-in-folio_expected_ref_count.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Bijan Tabatabai <bijan311(a)gmail.com> Subject: mm: consider non-anon swap cache folios in folio_expected_ref_count() Date: Tue, 16 Dec 2025 14:07:27 -0600 Currently, folio_expected_ref_count() only adds references for the swap cache if the folio is anonymous. However, according to the comment above the definition of PG_swapcache in enum pageflags, shmem folios can also have PG_swapcache set. This patch makes sure references for the swap cache are added if folio_test_swapcache(folio) is true. This issue was found when trying to hot-unplug memory in a QEMU/KVM virtual machine. When initiating hot-unplug when most of the guest memory is allocated, hot-unplug hangs partway through removal due to migration failures. The following message would be printed several times, and would be printed again about every five seconds: [ 49.641309] migrating pfn b12f25 failed ret:7 [ 49.641310] page: refcount:2 mapcount:0 mapping:0000000033bd8fe2 index:0x7f404d925 pfn:0xb12f25 [ 49.641311] aops:swap_aops [ 49.641313] flags: 0x300000000030508(uptodate|active|owner_priv_1|reclaim|swapbacked|node=0|zone=3) [ 49.641314] raw: 0300000000030508 ffffed312c4bc908 ffffed312c4bc9c8 0000000000000000 [ 49.641315] raw: 00000007f404d925 00000000000c823b 00000002ffffffff 0000000000000000 [ 49.641315] page dumped because: migration failure When debugging this, I found that these migration failures were due to __migrate_folio() returning -EAGAIN for a small set of folios because the expected reference count it calculates via folio_expected_ref_count() is one less than the actual reference count of the folios. Furthermore, all of the affected folios were not anonymous, but had the PG_swapcache flag set, inspiring this patch. After applying this patch, the memory hot-unplug behaves as expected. I tested this on a machine running Ubuntu 24.04 with kernel version 6.8.0-90-generic and 64GB of memory. The guest VM is managed by libvirt and runs Ubuntu 24.04 with kernel version 6.18 (though the head of the mm-unstable branch as a Dec 16, 2025 was also tested and behaves the same) and 48GB of memory. The libvirt XML definition for the VM can be found at [1]. CONFIG_MHP_DEFAULT_ONLINE_TYPE_ONLINE_MOVABLE is set in the guest kernel so the hot-pluggable memory is automatically onlined. Below are the steps to reproduce this behavior: 1) Define and start and virtual machine host$ virsh -c qemu:///system define ./test_vm.xml # test_vm.xml from [1] host$ virsh -c qemu:///system start test_vm 2) Setup swap in the guest guest$ sudo fallocate -l 32G /swapfile guest$ sudo chmod 0600 /swapfile guest$ sudo mkswap /swapfile guest$ sudo swapon /swapfile 3) Use alloc_data [2] to allocate most of the remaining guest memory guest$ ./alloc_data 45 4) In a separate guest terminal, monitor the amount of used memory guest$ watch -n1 free -h 5) When alloc_data has finished allocating, initiate the memory hot-unplug using the provided xml file [3] host$ virsh -c qemu:///system detach-device test_vm ./remove.xml --live After initiating the memory hot-unplug, you should see the amount of available memory in the guest decrease, and the amount of used swap data increase. If everything works as expected, when all of the memory is unplugged, there should be around 8.5-9GB of data in swap. If the unplugging is unsuccessful, the amount of used swap data will settle below that. If that happens, you should be able to see log messages in dmesg similar to the one posted above. Link: https://lkml.kernel.org/r/20251216200727.2360228-1-bijan311@gmail.com Link: https://github.com/BijanT/linux_patch_files/blob/main/test_vm.xml [1] Link: https://github.com/BijanT/linux_patch_files/blob/main/alloc_data.c [2] Link: https://github.com/BijanT/linux_patch_files/blob/main/remove.xml [3] Fixes: 86ebd50224c0 ("mm: add folio_expected_ref_count() for reference count calculation") Signed-off-by: Bijan Tabatabai <bijan311(a)gmail.com> Acked-by: David Hildenbrand (Red Hat) <david(a)kernel.org> Acked-by: Zi Yan <ziy(a)nvidia.com> Reviewed-by: Baolin Wang <baolin.wang(a)linux.alibaba.com> Cc: Liam Howlett <liam.howlett(a)oracle.com> Cc: Lorenzo Stoakes <lorenzo.stoakes(a)oracle.com> Cc: Michal Hocko <mhocko(a)suse.com> Cc: Mike Rapoport <rppt(a)kernel.org> Cc: Shivank Garg <shivankg(a)amd.com> Cc: Suren Baghdasaryan <surenb(a)google.com> Cc: Vlastimil Babka <vbabka(a)suse.cz> Cc: Kairui Song <ryncsn(a)gmail.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- include/linux/mm.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/include/linux/mm.h~mm-consider-non-anon-swap-cache-folios-in-folio_expected_ref_count +++ a/include/linux/mm.h @@ -2459,10 +2459,10 @@ static inline int folio_expected_ref_cou if (WARN_ON_ONCE(page_has_type(&folio->page) && !folio_test_hugetlb(folio))) return 0; - if (folio_test_anon(folio)) { - /* One reference per page from the swapcache. */ - ref_count += folio_test_swapcache(folio) << order; - } else { + /* One reference per page from the swapcache. */ + ref_count += folio_test_swapcache(folio) << order; + + if (!folio_test_anon(folio)) { /* One reference per page from the pagecache. */ ref_count += !!folio->mapping << order; /* One reference from PG_private. */ _ Patches currently in -mm which might be from bijan311(a)gmail.com are

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[merged mm-hotfixes-stable] rust-maple_tree-rcu_read_lock-in-destructor-to-silence-lockdep.patch removed from -mm tree

by Andrew Morton

The quilt patch titled Subject: rust: maple_tree: rcu_read_lock() in destructor to silence lockdep has been removed from the -mm tree. Its filename was rust-maple_tree-rcu_read_lock-in-destructor-to-silence-lockdep.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Alice Ryhl <aliceryhl(a)google.com> Subject: rust: maple_tree: rcu_read_lock() in destructor to silence lockdep Date: Wed, 17 Dec 2025 13:10:37 +0000 When running the Rust maple tree kunit tests with lockdep, you may trigger a warning that looks like this: lib/maple_tree.c:780 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 no locks held by kunit_try_catch/344. stack backtrace: CPU: 3 UID: 0 PID: 344 Comm: kunit_try_catch Tainted: G N 6.19.0-rc1+ #2 NONE Tainted: [N]=TEST Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x71/0x90 lockdep_rcu_suspicious+0x150/0x190 mas_start+0x104/0x150 mas_find+0x179/0x240 _RINvNtCs5QSdWC790r4_4core3ptr13drop_in_placeINtNtCs1cdwasc6FUb_6kernel10maple_tree9MapleTreeINtNtNtBL_5alloc4kbox3BoxlNtNtB1x_9allocator7KmallocEEECsgxAQYCfdR72_25doctests_kernel_generated+0xaf/0x130 rust_doctest_kernel_maple_tree_rs_0+0x600/0x6b0 ? lock_release+0xeb/0x2a0 ? kunit_try_catch_run+0x210/0x210 kunit_try_run_case+0x74/0x160 ? kunit_try_catch_run+0x210/0x210 kunit_generic_run_threadfn_adapter+0x12/0x30 kthread+0x21c/0x230 ? __do_trace_sched_kthread_stop_ret+0x40/0x40 ret_from_fork+0x16c/0x270 ? __do_trace_sched_kthread_stop_ret+0x40/0x40 ret_from_fork_asm+0x11/0x20 </TASK> This is because the destructor of maple tree calls mas_find() without taking rcu_read_lock() or the spinlock. Doing that is actually ok in this case since the destructor has exclusive access to the entire maple tree, but it triggers a lockdep warning. To fix that, take the rcu read lock. In the future, it's possible that memory reclaim could gain a feature where it reallocates entries in maple trees even if no user-code is touching it. If that feature is added, then this use of rcu read lock would become load-bearing, so I did not make it conditional on lockdep. We have to repeatedly take and release rcu because the destructor of T might perform operations that sleep. Link: https://lkml.kernel.org/r/20251217-maple-drop-rcu-v1-1-702af063573f@google.… Fixes: da939ef4c494 ("rust: maple_tree: add MapleTree") Signed-off-by: Alice Ryhl <aliceryhl(a)google.com> Reported-by: Andreas Hindborg <a.hindborg(a)kernel.org> Closes: https://rust-for-linux.zulipchat.com/#narrow/channel/x/topic/x/near/5642151… Reviewed-by: Gary Guo <gary(a)garyguo.net> Reviewed-by: Daniel Almeida <daniel.almeida(a)collabora.com> Cc: Andrew Ballance <andrewjballance(a)gmail.com> Cc: Bj��rn Roy Baron <bjorn3_gh(a)protonmail.com> Cc: Boqun Feng <boqun.feng(a)gmail.com> Cc: Danilo Krummrich <dakr(a)kernel.org> Cc: Liam Howlett <liam.howlett(a)oracle.com> Cc: Matthew Wilcox (Oracle) <willy(a)infradead.org> Cc: Miguel Ojeda <ojeda(a)kernel.org> Cc: Trevor Gross <tmgross(a)umich.edu> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- rust/kernel/maple_tree.rs | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) --- a/rust/kernel/maple_tree.rs~rust-maple_tree-rcu_read_lock-in-destructor-to-silence-lockdep +++ a/rust/kernel/maple_tree.rs @@ -265,7 +265,16 @@ impl<T: ForeignOwnable> MapleTree<T> { loop { // This uses the raw accessor because we're destroying pointers without removing them // from the maple tree, which is only valid because this is the destructor. - let ptr = ma_state.mas_find_raw(usize::MAX); + // + // Take the rcu lock because mas_find_raw() requires that you hold either the spinlock + // or the rcu read lock. This is only really required if memory reclaim might + // reallocate entries in the tree, as we otherwise have exclusive access. That feature + // doesn't exist yet, so for now, taking the rcu lock only serves the purpose of + // silencing lockdep. + let ptr = { + let _rcu = kernel::sync::rcu::Guard::new(); + ma_state.mas_find_raw(usize::MAX) + }; if ptr.is_null() { break; } _ Patches currently in -mm which might be from aliceryhl(a)google.com are

21 hours, 50 minutes

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[merged mm-hotfixes-stable] tools-mm-page_owner_sort-fix-timestamp-comparison-for-stable-sorting.patch removed from -mm tree

by Andrew Morton

The quilt patch titled Subject: tools/mm/page_owner_sort: fix timestamp comparison for stable sorting has been removed from the -mm tree. Its filename was tools-mm-page_owner_sort-fix-timestamp-comparison-for-stable-sorting.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Kaushlendra Kumar <kaushlendra.kumar(a)intel.com> Subject: tools/mm/page_owner_sort: fix timestamp comparison for stable sorting Date: Tue, 9 Dec 2025 10:15:52 +0530 The ternary operator in compare_ts() returns 1 when timestamps are equal, causing unstable sorting behavior. Replace with explicit three-way comparison that returns 0 for equal timestamps, ensuring stable qsort ordering and consistent output. Link: https://lkml.kernel.org/r/20251209044552.3396468-1-kaushlendra.kumar@intel.… Fixes: 8f9c447e2e2b ("tools/vm/page_owner_sort.c: support sorting pid and time") Signed-off-by: Kaushlendra Kumar <kaushlendra.kumar(a)intel.com> Cc: Chongxi Zhao <zhaochongxi2019(a)email.szu.edu.cn> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- tools/mm/page_owner_sort.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- a/tools/mm/page_owner_sort.c~tools-mm-page_owner_sort-fix-timestamp-comparison-for-stable-sorting +++ a/tools/mm/page_owner_sort.c @@ -181,7 +181,11 @@ static int compare_ts(const void *p1, co { const struct block_list *l1 = p1, *l2 = p2; - return l1->ts_nsec < l2->ts_nsec ? -1 : 1; + if (l1->ts_nsec < l2->ts_nsec) + return -1; + if (l1->ts_nsec > l2->ts_nsec) + return 1; + return 0; } static int compare_cull_condition(const void *p1, const void *p2) _ Patches currently in -mm which might be from kaushlendra.kumar(a)intel.com are tools-mm-thp_swap_allocator_test-fix-small-folio-alignment.patch tools-mm-slabinfo-fix-partial-long-option-mapping.patch

21 hours, 50 minutes

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[merged mm-hotfixes-stable] selftests-mm-fix-thread-state-check-in-uffd-unit-tests.patch removed from -mm tree

by Andrew Morton

The quilt patch titled Subject: selftests/mm: fix thread state check in uffd-unit-tests has been removed from the -mm tree. Its filename was selftests-mm-fix-thread-state-check-in-uffd-unit-tests.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Wake Liu <wakel(a)google.com> Subject: selftests/mm: fix thread state check in uffd-unit-tests Date: Wed, 10 Dec 2025 17:14:08 +0800 In the thread_state_get() function, the logic to find the thread's state character was using `sizeof(header) - 1` to calculate the offset from the "State:\t" string. The `header` variable is a `const char *` pointer. `sizeof()` on a pointer returns the size of the pointer itself, not the length of the string literal it points to. This makes the code's behavior dependent on the architecture's pointer size. This bug was identified on a 32-bit ARM build (`gsi_tv_arm`) for Android, running on an ARMv8-based device, compiled with Clang 19.0.1. On this 32-bit architecture, `sizeof(char *)` is 4. The expression `sizeof(header) - 1` resulted in an incorrect offset of 3, causing the test to read the wrong character from `/proc/[tid]/status` and fail. On 64-bit architectures, `sizeof(char *)` is 8, so the expression coincidentally evaluates to 7, which matches the length of "State:\t". This is why the bug likely remained hidden on 64-bit builds. To fix this and make the code portable and correct across all architectures, this patch replaces `sizeof(header) - 1` with `strlen(header)`. The `strlen()` function correctly calculates the string's length, ensuring the correct offset is always used. Link: https://lkml.kernel.org/r/20251210091408.3781445-1-wakel@google.com Fixes: f60b6634cd88 ("mm/selftests: add a test to verify mmap_changing race with -EAGAIN") Signed-off-by: Wake Liu <wakel(a)google.com> Acked-by: Peter Xu <peterx(a)redhat.com> Reviewed-by: Mike Rapoport (Microsoft) <rppt(a)kernel.org> Cc: Bill Wendling <morbo(a)google.com> Cc: Justin Stitt <justinstitt(a)google.com> Cc: Liam Howlett <liam.howlett(a)oracle.com> Cc: Lorenzo Stoakes <lorenzo.stoakes(a)oracle.com> Cc: Michal Hocko <mhocko(a)suse.com> Cc: Nathan Chancellor <nathan(a)kernel.org> Cc: Shuah Khan <shuah(a)kernel.org> Cc: Suren Baghdasaryan <surenb(a)google.com> Cc: Vlastimil Babka <vbabka(a)suse.cz> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- tools/testing/selftests/mm/uffd-unit-tests.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/tools/testing/selftests/mm/uffd-unit-tests.c~selftests-mm-fix-thread-state-check-in-uffd-unit-tests +++ a/tools/testing/selftests/mm/uffd-unit-tests.c @@ -1317,7 +1317,7 @@ static thread_state thread_state_get(pid p = strstr(tmp, header); if (p) { /* For example, "State:\tD (disk sleep)" */ - c = *(p + sizeof(header) - 1); + c = *(p + strlen(header)); return c == 'D' ? THR_STATE_UNINTERRUPTIBLE : THR_STATE_UNKNOWN; } _ Patches currently in -mm which might be from wakel(a)google.com are

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