Add tracking of pages that were pinned via FOLL_PIN.
As mentioned in the FOLL_PIN documentation, callers who effectively set FOLL_PIN are required to ultimately free such pages via put_user_page(). The effect is similar to FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use".
Pages that have been pinned via FOLL_PIN are identifiable via a new function call:
bool page_dma_pinned(struct page *page);
What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1].
This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask().
Suggested-by: Jan Kara jack@suse.cz Suggested-by: Jérôme Glisse jglisse@redhat.com Signed-off-by: John Hubbard jhubbard@nvidia.com --- include/linux/mm.h | 74 +++++++++++---- include/linux/mmzone.h | 2 + include/linux/page_ref.h | 10 +++ mm/gup.c | 189 +++++++++++++++++++++++++++++++++------ mm/huge_memory.c | 54 ++++++++++- mm/hugetlb.c | 39 +++++++- mm/vmstat.c | 2 + 7 files changed, 321 insertions(+), 49 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h index c351e1b0b4b7..19b3fa68a4da 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1054,6 +1054,8 @@ static inline __must_check bool try_get_page(struct page *page) return true; }
+__must_check bool user_page_ref_inc(struct page *page); + static inline void put_page(struct page *page) { page = compound_head(page); @@ -1071,30 +1073,70 @@ static inline void put_page(struct page *page) __put_page(page); }
-/** - * put_user_page() - release a gup-pinned page - * @page: pointer to page to be released +/* + * GUP_PIN_COUNTING_BIAS, and the associated functions that use it, overload + * the page's refcount so that two separate items are tracked: the original page + * reference count, and also a new count of how many get_user_pages() calls were + * made against the page. ("gup-pinned" is another term for the latter). + * + * With this scheme, get_user_pages() becomes special: such pages are marked + * as distinct from normal pages. As such, the new put_user_page() call (and + * its variants) must be used in order to release gup-pinned pages. + * + * Choice of value: * - * Pages that were pinned via either pin_user_pages*() or pin_longterm_pages*() - * must be released via either put_user_page(), or one of the put_user_pages*() - * routines. This is so that eventually such pages can be separately tracked and - * uniquely handled. In particular, interactions with RDMA and filesystems need - * special handling. + * By making GUP_PIN_COUNTING_BIAS a power of two, debugging of page reference + * counts with respect to get_user_pages() and put_user_page() becomes simpler, + * due to the fact that adding an even power of two to the page refcount has + * the effect of using only the upper N bits, for the code that counts up using + * the bias value. This means that the lower bits are left for the exclusive + * use of the original code that increments and decrements by one (or at least, + * by much smaller values than the bias value). * - * put_user_page() and put_page() are not interchangeable, despite this early - * implementation that makes them look the same. put_user_page() calls must - * be perfectly matched up with pin*() calls. + * Of course, once the lower bits overflow into the upper bits (and this is + * OK, because subtraction recovers the original values), then visual inspection + * no longer suffices to directly view the separate counts. However, for normal + * applications that don't have huge page reference counts, this won't be an + * issue. + * + * Locking: the lockless algorithm described in page_cache_get_speculative() + * and page_cache_gup_pin_speculative() provides safe operation for + * get_user_pages and page_mkclean and other calls that race to set up page + * table entries. */ -static inline void put_user_page(struct page *page) -{ - put_page(page); -} +#define GUP_PIN_COUNTING_BIAS (1UL << 10)
+void put_user_page(struct page *page); void put_user_pages_dirty_lock(struct page **pages, unsigned long npages, bool make_dirty); - void put_user_pages(struct page **pages, unsigned long npages);
+/** + * page_dma_pinned() - report if a page is pinned for DMA. + * + * This function checks if a page has been pinned via a call to + * pin_user_pages*() or pin_longterm_pages*(). + * + * The return value is partially fuzzy: false is not fuzzy, because it means + * "definitely not pinned for DMA", but true means "probably pinned for DMA, but + * possibly a false positive due to having at least GUP_PIN_COUNTING_BIAS worth + * of normal page references". + * + * False positives are OK, because: a) it's unlikely for a page to get that many + * refcounts, and b) all the callers of this routine are expected to be able to + * deal gracefully with a false positive. + * + * For more information, please see Documentation/vm/pin_user_pages.rst. + * + * @page: pointer to page to be queried. + * @Return: True, if it is likely that the page has been "dma-pinned". + * False, if the page is definitely not dma-pinned. + */ +static inline bool page_dma_pinned(struct page *page) +{ + return (page_ref_count(compound_head(page))) >= GUP_PIN_COUNTING_BIAS; +} + #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP) #define SECTION_IN_PAGE_FLAGS #endif diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index bda20282746b..0485cba38d23 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -244,6 +244,8 @@ enum node_stat_item { NR_DIRTIED, /* page dirtyings since bootup */ NR_WRITTEN, /* page writings since bootup */ NR_KERNEL_MISC_RECLAIMABLE, /* reclaimable non-slab kernel pages */ + NR_FOLL_PIN_REQUESTED, /* via: pin_user_page(), gup flag: FOLL_PIN */ + NR_FOLL_PIN_RETURNED, /* pages returned via put_user_page() */ NR_VM_NODE_STAT_ITEMS };
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h index 14d14beb1f7f..b9cbe553d1e7 100644 --- a/include/linux/page_ref.h +++ b/include/linux/page_ref.h @@ -102,6 +102,16 @@ static inline void page_ref_sub(struct page *page, int nr) __page_ref_mod(page, -nr); }
+static inline int page_ref_sub_return(struct page *page, int nr) +{ + int ret = atomic_sub_return(nr, &page->_refcount); + + if (page_ref_tracepoint_active(__tracepoint_page_ref_mod)) + __page_ref_mod(page, -nr); + + return ret; +} + static inline void page_ref_inc(struct page *page) { atomic_inc(&page->_refcount); diff --git a/mm/gup.c b/mm/gup.c index 4409e84dff51..82e7e4ce5027 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -51,6 +51,94 @@ static inline struct page *try_get_compound_head(struct page *page, int refs) return head; }
+#ifdef CONFIG_DEBUG_VM +static inline void __update_proc_vmstat(struct page *page, + enum node_stat_item item, int count) +{ + mod_node_page_state(page_pgdat(page), item, count); +} +#else +static inline void __update_proc_vmstat(struct page *page, + enum node_stat_item item, int count) +{ +} +#endif + +/** + * user_page_ref_inc() - mark a page as being used by get_user_pages(FOLL_PIN). + * + * @page: pointer to page to be marked + * @Return: true for success, false for failure + */ +__must_check bool user_page_ref_inc(struct page *page) +{ + page = try_get_compound_head(page, GUP_PIN_COUNTING_BIAS); + if (!page) + return false; + + __update_proc_vmstat(page, NR_FOLL_PIN_REQUESTED, 1); + return true; +} + +#ifdef CONFIG_DEV_PAGEMAP_OPS +static bool __put_devmap_managed_user_page(struct page *page) +{ + bool is_devmap = page_is_devmap_managed(page); + + if (is_devmap) { + int count = page_ref_sub_return(page, GUP_PIN_COUNTING_BIAS); + + __update_proc_vmstat(page, NR_FOLL_PIN_RETURNED, 1); + /* + * devmap page refcounts are 1-based, rather than 0-based: if + * refcount is 1, then the page is free and the refcount is + * stable because nobody holds a reference on the page. + */ + if (count == 1) + free_devmap_managed_page(page); + else if (!count) + __put_page(page); + } + + return is_devmap; +} +#else +static bool __put_devmap_managed_user_page(struct page *page) +{ + return false; +} +#endif /* CONFIG_DEV_PAGEMAP_OPS */ + +/** + * put_user_page() - release a dma-pinned page + * @page: pointer to page to be released + * + * Pages that were pinned via either pin_user_pages*() or pin_longterm_pages*() + * must be released via either put_user_page(), or one of the put_user_pages*() + * routines. This is so that such pages can be separately tracked and uniquely + * handled. In particular, interactions with RDMA and filesystems need special + * handling. + */ +void put_user_page(struct page *page) +{ + page = compound_head(page); + + /* + * For devmap managed pages we need to catch refcount transition from + * GUP_PIN_COUNTING_BIAS to 1, when refcount reach one it means the + * page is free and we need to inform the device driver through + * callback. See include/linux/memremap.h and HMM for details. + */ + if (__put_devmap_managed_user_page(page)) + return; + + if (page_ref_sub_and_test(page, GUP_PIN_COUNTING_BIAS)) + __put_page(page); + + __update_proc_vmstat(page, NR_FOLL_PIN_RETURNED, 1); +} +EXPORT_SYMBOL(put_user_page); + /** * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages * @pages: array of pages to be maybe marked dirty, and definitely released. @@ -237,10 +325,11 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, }
page = vm_normal_page(vma, address, pte); - if (!page && pte_devmap(pte) && (flags & FOLL_GET)) { + if (!page && pte_devmap(pte) && (flags & (FOLL_GET | FOLL_PIN))) { /* - * Only return device mapping pages in the FOLL_GET case since - * they are only valid while holding the pgmap reference. + * Only return device mapping pages in the FOLL_GET or FOLL_PIN + * case since they are only valid while holding the pgmap + * reference. */ *pgmap = get_dev_pagemap(pte_pfn(pte), *pgmap); if (*pgmap) @@ -283,6 +372,11 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, page = ERR_PTR(-ENOMEM); goto out; } + } else if (flags & FOLL_PIN) { + if (unlikely(!user_page_ref_inc(page))) { + page = ERR_PTR(-ENOMEM); + goto out; + } } if (flags & FOLL_TOUCH) { if ((flags & FOLL_WRITE) && @@ -544,8 +638,8 @@ static struct page *follow_page_mask(struct vm_area_struct *vma, /* make this handle hugepd */ page = follow_huge_addr(mm, address, flags & FOLL_WRITE); if (!IS_ERR(page)) { - BUG_ON(flags & FOLL_GET); - return page; + WARN_ON_ONCE(flags & (FOLL_GET | FOLL_PIN)); + return NULL; }
pgd = pgd_offset(mm, address); @@ -1844,13 +1938,17 @@ static inline pte_t gup_get_pte(pte_t *ptep) #endif /* CONFIG_GUP_GET_PTE_LOW_HIGH */
static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start, + unsigned int flags, struct page **pages) { while ((*nr) - nr_start) { struct page *page = pages[--(*nr)];
ClearPageReferenced(page); - put_page(page); + if (flags & FOLL_PIN) + put_user_page(page); + else + put_page(page); } }
@@ -1883,7 +1981,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
pgmap = get_dev_pagemap(pte_pfn(pte), pgmap); if (unlikely(!pgmap)) { - undo_dev_pagemap(nr, nr_start, pages); + undo_dev_pagemap(nr, nr_start, flags, pages); goto pte_unmap; } } else if (pte_special(pte)) @@ -1892,9 +1990,15 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page = pte_page(pte);
- head = try_get_compound_head(page, 1); - if (!head) - goto pte_unmap; + if (flags & FOLL_PIN) { + head = page; + if (unlikely(!user_page_ref_inc(head))) + goto pte_unmap; + } else { + head = try_get_compound_head(page, 1); + if (!head) + goto pte_unmap; + }
if (unlikely(pte_val(pte) != pte_val(*ptep))) { put_page(head); @@ -1948,12 +2052,20 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
pgmap = get_dev_pagemap(pfn, pgmap); if (unlikely(!pgmap)) { - undo_dev_pagemap(nr, nr_start, pages); + undo_dev_pagemap(nr, nr_start, flags, pages); return 0; } SetPageReferenced(page); pages[*nr] = page; - get_page(page); + + if (flags & FOLL_PIN) { + if (unlikely(!user_page_ref_inc(page))) { + undo_dev_pagemap(nr, nr_start, flags, pages); + return 0; + } + } else + get_page(page); + (*nr)++; pfn++; } while (addr += PAGE_SIZE, addr != end); @@ -1975,7 +2087,7 @@ static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, return 0;
if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) { - undo_dev_pagemap(nr, nr_start, pages); + undo_dev_pagemap(nr, nr_start, flags, pages); return 0; } return 1; @@ -1993,7 +2105,7 @@ static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, return 0;
if (unlikely(pud_val(orig) != pud_val(*pudp))) { - undo_dev_pagemap(nr, nr_start, pages); + undo_dev_pagemap(nr, nr_start, flags, pages); return 0; } return 1; @@ -2077,9 +2189,16 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, page = head + ((addr & (sz-1)) >> PAGE_SHIFT); refs = __record_subpages(page, addr, end, pages, *nr);
- head = try_get_compound_head(head, refs); - if (!head) - return 0; + if (flags & FOLL_PIN) { + head = page; + if (unlikely(!user_page_ref_inc(head))) + return 0; + head = page; + } else { + head = try_get_compound_head(head, refs); + if (!head) + return 0; + }
if (unlikely(pte_val(pte) != pte_val(*ptep))) { put_compound_head(head, refs); @@ -2136,9 +2255,15 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT); refs = __record_subpages(page, addr, end, pages, *nr);
- head = try_get_compound_head(pmd_page(orig), refs); - if (!head) - return 0; + if (flags & FOLL_PIN) { + head = page; + if (unlikely(!user_page_ref_inc(head))) + return 0; + } else { + head = try_get_compound_head(pmd_page(orig), refs); + if (!head) + return 0; + }
if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) { put_compound_head(head, refs); @@ -2169,9 +2294,15 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT); refs = __record_subpages(page, addr, end, pages, *nr);
- head = try_get_compound_head(pud_page(orig), refs); - if (!head) - return 0; + if (flags & FOLL_PIN) { + head = page; + if (unlikely(!user_page_ref_inc(head))) + return 0; + } else { + head = try_get_compound_head(pud_page(orig), refs); + if (!head) + return 0; + }
if (unlikely(pud_val(orig) != pud_val(*pudp))) { put_compound_head(head, refs); @@ -2197,9 +2328,15 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT); refs = __record_subpages(page, addr, end, pages, *nr);
- head = try_get_compound_head(pgd_page(orig), refs); - if (!head) - return 0; + if (flags & FOLL_PIN) { + head = page; + if (unlikely(!user_page_ref_inc(head))) + return 0; + } else { + head = try_get_compound_head(pgd_page(orig), refs); + if (!head) + return 0; + }
if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) { put_compound_head(head, refs); diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 13cc93785006..4010c269e9e5 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -945,6 +945,11 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr, */ WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");
+ /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == + (FOLL_PIN | FOLL_GET))) + return NULL; + if (flags & FOLL_WRITE && !pmd_write(*pmd)) return NULL;
@@ -960,7 +965,7 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr, * device mapped pages can only be returned if the * caller will manage the page reference count. */ - if (!(flags & FOLL_GET)) + if (!(flags & (FOLL_GET | FOLL_PIN))) return ERR_PTR(-EEXIST);
pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT; @@ -968,7 +973,18 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr, if (!*pgmap) return ERR_PTR(-EFAULT); page = pfn_to_page(pfn); - get_page(page); + + if (flags & FOLL_GET) + get_page(page); + else if (flags & FOLL_PIN) { + /* + * user_page_ref_inc() is not actually expected to fail here + * because we hold the pmd lock so no one can unmap the pmd and + * free the page that it points to. + */ + if (unlikely(!user_page_ref_inc(page))) + page = ERR_PTR(-EFAULT); + }
return page; } @@ -1088,6 +1104,11 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr, if (flags & FOLL_WRITE && !pud_write(*pud)) return NULL;
+ /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == + (FOLL_PIN | FOLL_GET))) + return NULL; + if (pud_present(*pud) && pud_devmap(*pud)) /* pass */; else @@ -1099,8 +1120,10 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr, /* * device mapped pages can only be returned if the * caller will manage the page reference count. + * + * At least one of FOLL_GET | FOLL_PIN must be set, so assert that here: */ - if (!(flags & FOLL_GET)) + if (!(flags & (FOLL_GET | FOLL_PIN))) return ERR_PTR(-EEXIST);
pfn += (addr & ~PUD_MASK) >> PAGE_SHIFT; @@ -1108,7 +1131,18 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr, if (!*pgmap) return ERR_PTR(-EFAULT); page = pfn_to_page(pfn); - get_page(page); + + if (flags & FOLL_GET) + get_page(page); + else if (flags & FOLL_PIN) { + /* + * user_page_ref_inc() is not actually expected to fail here + * because we hold the pud lock so no one can unmap the pud and + * free the page that it points to. + */ + if (unlikely(!user_page_ref_inc(page))) + page = ERR_PTR(-EFAULT); + }
return page; } @@ -1522,8 +1556,20 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma, skip_mlock: page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT; VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page); + if (flags & FOLL_GET) get_page(page); + else if (flags & FOLL_PIN) { + /* + * user_page_ref_inc() is not actually expected to fail here + * because we hold the pmd lock so no one can unmap the pmd and + * free the page that it points to. + */ + if (unlikely(!user_page_ref_inc(page))) { + WARN_ON_ONCE(1); + page = NULL; + } + }
out: return page; diff --git a/mm/hugetlb.c b/mm/hugetlb.c index b45a95363a84..5ee80eea25e5 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4462,7 +4462,22 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, same_page: if (pages) { pages[i] = mem_map_offset(page, pfn_offset); - get_page(pages[i]); + + if (flags & FOLL_GET) + get_page(pages[i]); + else if (flags & FOLL_PIN) { + /* + * user_page_ref_inc() is not actually expected + * to fail here because we hold the ptl. + */ + if (unlikely(!user_page_ref_inc(pages[i]))) { + spin_unlock(ptl); + remainder = 0; + err = -ENOMEM; + WARN_ON_ONCE(1); + break; + } + } }
if (vmas) @@ -5022,6 +5037,12 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, struct page *page = NULL; spinlock_t *ptl; pte_t pte; + + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == + (FOLL_PIN | FOLL_GET))) + return NULL; + retry: ptl = pmd_lockptr(mm, pmd); spin_lock(ptl); @@ -5034,8 +5055,20 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, pte = huge_ptep_get((pte_t *)pmd); if (pte_present(pte)) { page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT); + if (flags & FOLL_GET) get_page(page); + else if (flags & FOLL_PIN) { + /* + * user_page_ref_inc() is not actually expected to fail + * here because we hold the ptl. + */ + if (unlikely(!user_page_ref_inc(page))) { + WARN_ON_ONCE(1); + page = NULL; + goto out; + } + } } else { if (is_hugetlb_entry_migration(pte)) { spin_unlock(ptl); @@ -5056,7 +5089,7 @@ struct page * __weak follow_huge_pud(struct mm_struct *mm, unsigned long address, pud_t *pud, int flags) { - if (flags & FOLL_GET) + if (flags & (FOLL_GET | FOLL_PIN)) return NULL;
return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT); @@ -5065,7 +5098,7 @@ follow_huge_pud(struct mm_struct *mm, unsigned long address, struct page * __weak follow_huge_pgd(struct mm_struct *mm, unsigned long address, pgd_t *pgd, int flags) { - if (flags & FOLL_GET) + if (flags & (FOLL_GET | FOLL_PIN)) return NULL;
return pte_page(*(pte_t *)pgd) + ((address & ~PGDIR_MASK) >> PAGE_SHIFT); diff --git a/mm/vmstat.c b/mm/vmstat.c index a8222041bd44..fdad40ccde7b 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1167,6 +1167,8 @@ const char * const vmstat_text[] = { "nr_dirtied", "nr_written", "nr_kernel_misc_reclaimable", + "nr_foll_pin_requested", + "nr_foll_pin_returned",
/* enum writeback_stat_item counters */ "nr_dirty_threshold",