5.10-stable review patch. If anyone has any objections, please let me know.
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From: James Houghton jthoughton@google.com
commit b30c14cd61025eeea2f2e8569606cd167ba9ad2d upstream.
PMD sharing can only be done in PUD_SIZE-aligned pieces of VMAs; however, it is possible that HugeTLB VMAs are split without unsharing the PMDs first.
Without this fix, it is possible to hit the uffd-wp-related WARN_ON_ONCE in hugetlb_change_protection [1]. The key there is that hugetlb_unshare_all_pmds will not attempt to unshare PMDs in non-PUD_SIZE-aligned sections of the VMA.
It might seem ideal to unshare in hugetlb_vm_op_open, but we need to unshare in both the new and old VMAs, so unsharing in hugetlb_vm_op_split seems natural.
[1]: https://lore.kernel.org/linux-mm/CADrL8HVeOkj0QH5VZZbRzybNE8CG-tEGFshnA+bG9n...
Link: https://lkml.kernel.org/r/20230104231910.1464197-1-jthoughton@google.com Fixes: 6dfeaff93be1 ("hugetlb/userfaultfd: unshare all pmds for hugetlbfs when register wp") Signed-off-by: James Houghton jthoughton@google.com Reviewed-by: Mike Kravetz mike.kravetz@oracle.com Acked-by: Peter Xu peterx@redhat.com Cc: Axel Rasmussen axelrasmussen@google.com Cc: Muchun Song songmuchun@bytedance.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org [backport notes: I believe the "Fixes" tag is somewhat wrong - kernels before that commit already had an adjust_range_if_pmd_sharing_possible() that assumes that shared PMDs can't straddle page table boundaries. huge_pmd_unshare() takes different parameter type] Signed-off-by: Jann Horn jannh@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/hugetlb.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 65 insertions(+)
--- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -96,6 +96,8 @@ static inline void ClearPageHugeFreed(st
/* Forward declaration */ static int hugetlb_acct_memory(struct hstate *h, long delta); +static void hugetlb_unshare_pmds(struct vm_area_struct *vma, + unsigned long start, unsigned long end);
static inline void unlock_or_release_subpool(struct hugepage_subpool *spool) { @@ -3697,6 +3699,25 @@ static int hugetlb_vm_op_split(struct vm { if (addr & ~(huge_page_mask(hstate_vma(vma)))) return -EINVAL; + + /* + * PMD sharing is only possible for PUD_SIZE-aligned address ranges + * in HugeTLB VMAs. If we will lose PUD_SIZE alignment due to this + * split, unshare PMDs in the PUD_SIZE interval surrounding addr now. + */ + if (addr & ~PUD_MASK) { + /* + * hugetlb_vm_op_split is called right before we attempt to + * split the VMA. We will need to unshare PMDs in the old and + * new VMAs, so let's unshare before we split. + */ + unsigned long floor = addr & PUD_MASK; + unsigned long ceil = floor + PUD_SIZE; + + if (floor >= vma->vm_start && ceil <= vma->vm_end) + hugetlb_unshare_pmds(vma, floor, ceil); + } + return 0; }
@@ -5706,6 +5727,50 @@ void move_hugetlb_state(struct page *old } }
+static void hugetlb_unshare_pmds(struct vm_area_struct *vma, + unsigned long start, + unsigned long end) +{ + struct hstate *h = hstate_vma(vma); + unsigned long sz = huge_page_size(h); + struct mm_struct *mm = vma->vm_mm; + struct mmu_notifier_range range; + unsigned long address; + spinlock_t *ptl; + pte_t *ptep; + + if (!(vma->vm_flags & VM_MAYSHARE)) + return; + + if (start >= end) + return; + + flush_cache_range(vma, start, end); + /* + * No need to call adjust_range_if_pmd_sharing_possible(), because + * we have already done the PUD_SIZE alignment. + */ + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, + start, end); + mmu_notifier_invalidate_range_start(&range); + i_mmap_lock_write(vma->vm_file->f_mapping); + for (address = start; address < end; address += PUD_SIZE) { + ptep = huge_pte_offset(mm, address, sz); + if (!ptep) + continue; + ptl = huge_pte_lock(h, mm, ptep); + huge_pmd_unshare(mm, vma, &address, ptep); + spin_unlock(ptl); + } + flush_hugetlb_tlb_range(vma, start, end); + i_mmap_unlock_write(vma->vm_file->f_mapping); + /* + * No need to call mmu_notifier_invalidate_range(), see + * Documentation/mm/mmu_notifier.rst. + */ + mmu_notifier_invalidate_range_end(&range); +} + #ifdef CONFIG_CMA static bool cma_reserve_called __initdata;