diff options
| -rw-r--r-- | include/linux/mm.h | 39 | ||||
| -rw-r--r-- | mm/gup.c | 42 | ||||
| -rw-r--r-- | mm/huge_memory.c | 3 | ||||
| -rw-r--r-- | mm/hugetlb.c | 27 |
4 files changed, 105 insertions, 6 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index 9ee3ae51e8e3..5dc5005ccc9b 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3002,6 +3002,45 @@ static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags) return 0; } +/* + * Indicates for which pages that are write-protected in the page table, + * whether GUP has to trigger unsharing via FAULT_FLAG_UNSHARE such that the + * GUP pin will remain consistent with the pages mapped into the page tables + * of the MM. + * + * Temporary unmapping of PageAnonExclusive() pages or clearing of + * PageAnonExclusive() has to protect against concurrent GUP: + * * Ordinary GUP: Using the PT lock + * * GUP-fast and fork(): mm->write_protect_seq + * * GUP-fast and KSM or temporary unmapping (swap, migration): + * clear/invalidate+flush of the page table entry + * + * Must be called with the (sub)page that's actually referenced via the + * page table entry, which might not necessarily be the head page for a + * PTE-mapped THP. + */ +static inline bool gup_must_unshare(unsigned int flags, struct page *page) +{ + /* + * FOLL_WRITE is implicitly handled correctly as the page table entry + * has to be writable -- and if it references (part of) an anonymous + * folio, that part is required to be marked exclusive. + */ + if ((flags & (FOLL_WRITE | FOLL_PIN)) != FOLL_PIN) + return false; + /* + * Note: PageAnon(page) is stable until the page is actually getting + * freed. + */ + if (!PageAnon(page)) + return false; + /* + * Note that PageKsm() pages cannot be exclusive, and consequently, + * cannot get pinned. + */ + return !PageAnonExclusive(page); +} + typedef int (*pte_fn_t)(pte_t *pte, unsigned long addr, void *data); extern int apply_to_page_range(struct mm_struct *mm, unsigned long address, unsigned long size, pte_fn_t fn, void *data); @@ -506,6 +506,10 @@ retry: } } + if (!pte_write(pte) && gup_must_unshare(flags, page)) { + page = ERR_PTR(-EMLINK); + goto out; + } /* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. */ if (unlikely(!try_grab_page(page, flags))) { page = ERR_PTR(-ENOMEM); @@ -732,6 +736,11 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma, * When getting pages from ZONE_DEVICE memory, the @ctx->pgmap caches * the device's dev_pagemap metadata to avoid repeating expensive lookups. * + * When getting an anonymous page and the caller has to trigger unsharing + * of a shared anonymous page first, -EMLINK is returned. The caller should + * trigger a fault with FAULT_FLAG_UNSHARE set. Note that unsharing is only + * relevant with FOLL_PIN and !FOLL_WRITE. + * * On output, the @ctx->page_mask is set according to the size of the page. * * Return: the mapped (struct page *), %NULL if no mapping exists, or @@ -855,7 +864,8 @@ unmap: * is, *@locked will be set to 0 and -EBUSY returned. */ static int faultin_page(struct vm_area_struct *vma, - unsigned long address, unsigned int *flags, int *locked) + unsigned long address, unsigned int *flags, bool unshare, + int *locked) { unsigned int fault_flags = 0; vm_fault_t ret; @@ -877,6 +887,11 @@ static int faultin_page(struct vm_area_struct *vma, */ fault_flags |= FAULT_FLAG_TRIED; } + if (unshare) { + fault_flags |= FAULT_FLAG_UNSHARE; + /* FAULT_FLAG_WRITE and FAULT_FLAG_UNSHARE are incompatible */ + VM_BUG_ON(fault_flags & FAULT_FLAG_WRITE); + } ret = handle_mm_fault(vma, address, fault_flags, NULL); if (ret & VM_FAULT_ERROR) { @@ -1098,8 +1113,9 @@ retry: cond_resched(); page = follow_page_mask(vma, start, foll_flags, &ctx); - if (!page) { - ret = faultin_page(vma, start, &foll_flags, locked); + if (!page || PTR_ERR(page) == -EMLINK) { + ret = faultin_page(vma, start, &foll_flags, + PTR_ERR(page) == -EMLINK, locked); switch (ret) { case 0: goto retry; @@ -2201,6 +2217,11 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, goto pte_unmap; } + if (!pte_write(pte) && gup_must_unshare(flags, page)) { + gup_put_folio(folio, 1, flags); + goto pte_unmap; + } + /* * We need to make the page accessible if and only if we are * going to access its content (the FOLL_PIN case). Please @@ -2381,6 +2402,11 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, return 0; } + if (!pte_write(pte) && gup_must_unshare(flags, &folio->page)) { + gup_put_folio(folio, refs, flags); + return 0; + } + *nr += refs; folio_set_referenced(folio); return 1; @@ -2442,6 +2468,11 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, return 0; } + if (!pmd_write(orig) && gup_must_unshare(flags, &folio->page)) { + gup_put_folio(folio, refs, flags); + return 0; + } + *nr += refs; folio_set_referenced(folio); return 1; @@ -2477,6 +2508,11 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, return 0; } + if (!pud_write(orig) && gup_must_unshare(flags, &folio->page)) { + gup_put_folio(folio, refs, flags); + return 0; + } + *nr += refs; folio_set_referenced(folio); return 1; diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 17ec6c939e7f..4414111998df 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1389,6 +1389,9 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma, page = pmd_page(*pmd); VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page); + if (!pmd_write(*pmd) && gup_must_unshare(flags, page)) + return ERR_PTR(-EMLINK); + if (!try_grab_page(page, flags)) return ERR_PTR(-ENOMEM); diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 9cefa3dd9af3..5f8d3a77a2ec 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5982,6 +5982,25 @@ static void record_subpages_vmas(struct page *page, struct vm_area_struct *vma, } } +static inline bool __follow_hugetlb_must_fault(unsigned int flags, pte_t *pte, + bool *unshare) +{ + pte_t pteval = huge_ptep_get(pte); + + *unshare = false; + if (is_swap_pte(pteval)) + return true; + if (huge_pte_write(pteval)) + return false; + if (flags & FOLL_WRITE) + return true; + if (gup_must_unshare(flags, pte_page(pteval))) { + *unshare = true; + return true; + } + return false; +} + long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, struct page **pages, struct vm_area_struct **vmas, unsigned long *position, unsigned long *nr_pages, @@ -5996,6 +6015,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, while (vaddr < vma->vm_end && remainder) { pte_t *pte; spinlock_t *ptl = NULL; + bool unshare = false; int absent; struct page *page; @@ -6046,9 +6066,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, * both cases, and because we can't follow correct pages * directly from any kind of swap entries. */ - if (absent || is_swap_pte(huge_ptep_get(pte)) || - ((flags & FOLL_WRITE) && - !huge_pte_write(huge_ptep_get(pte)))) { + if (absent || + __follow_hugetlb_must_fault(flags, pte, &unshare)) { vm_fault_t ret; unsigned int fault_flags = 0; @@ -6056,6 +6075,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, spin_unlock(ptl); if (flags & FOLL_WRITE) fault_flags |= FAULT_FLAG_WRITE; + else if (unshare) + fault_flags |= FAULT_FLAG_UNSHARE; if (locked) fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE; |