From 01d89b93e1769928529d339d6e4f780129454161 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Tue, 30 Apr 2024 09:13:03 -0400 Subject: [PATCH] mm/gup: fix hugepd handling in hugetlb rework Commit a12083d721d7 added hugepd handling for gup-slow, reusing gup-fast functions. follow_hugepd() correctly took the vma pointer in, however didn't pass it over into the lower functions, which was overlooked. The issue is gup_fast_hugepte() uses the vma pointer to make the correct decision on whether an unshare is needed for a FOLL_PIN|FOLL_LONGTERM. Now without vma ponter it will constantly return "true" (needs an unshare) for a page cache, even though in the SHARED case it will be wrong to unshare. The other problem is, even if an unshare is needed, it now returns 0 rather than -EMLINK, which will not trigger a follow up FAULT_FLAG_UNSHARE fault. That will need to be fixed too when the unshare is wanted. gup_longterm test didn't expose this issue in the past because it didn't yet test R/O unshare in this case, another separate patch will enable that in future tests. Fix it by passing vma correctly to the bottom, rename gup_fast_hugepte() back to gup_hugepte() as it is shared between the fast/slow paths, and also allow -EMLINK to be returned properly by gup_hugepte() even though gup-fast will take it the same as zero. Link: https://lkml.kernel.org/r/20240430131303.264331-1-peterx@redhat.com Fixes: a12083d721d7 ("mm/gup: handle hugepd for follow_page()") Signed-off-by: Peter Xu Reported-by: David Hildenbrand Reviewed-by: David Hildenbrand Cc: Aneesh Kumar K.V Cc: Christophe Leroy Cc: Jason Gunthorpe Cc: John Hubbard Cc: Lorenzo Stoakes Cc: Muchun Song Signed-off-by: Andrew Morton --- mm/gup.c | 64 ++++++++++++++++++++++++++++++++++---------------------- 1 file changed, 39 insertions(+), 25 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 2f7baf96f655..ca0f5cedce9b 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -525,9 +525,17 @@ static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end, return (__boundary - 1 < end - 1) ? __boundary : end; } -static int gup_fast_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, - unsigned long end, unsigned int flags, struct page **pages, - int *nr) +/* + * Returns 1 if succeeded, 0 if failed, -EMLINK if unshare needed. + * + * NOTE: for the same entry, gup-fast and gup-slow can return different + * results (0 v.s. -EMLINK) depending on whether vma is available. This is + * the expected behavior, where we simply want gup-fast to fallback to + * gup-slow to take the vma reference first. + */ +static int gup_hugepte(struct vm_area_struct *vma, pte_t *ptep, unsigned long sz, + unsigned long addr, unsigned long end, unsigned int flags, + struct page **pages, int *nr) { unsigned long pte_end; struct page *page; @@ -559,9 +567,9 @@ static int gup_fast_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, return 0; } - if (!pte_write(pte) && gup_must_unshare(NULL, flags, &folio->page)) { + if (!pte_write(pte) && gup_must_unshare(vma, flags, &folio->page)) { gup_put_folio(folio, refs, flags); - return 0; + return -EMLINK; } *nr += refs; @@ -577,19 +585,22 @@ static int gup_fast_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, * of the other folios. See writable_file_mapping_allowed() and * gup_fast_folio_allowed() for more information. */ -static int gup_fast_hugepd(hugepd_t hugepd, unsigned long addr, - unsigned int pdshift, unsigned long end, unsigned int flags, - struct page **pages, int *nr) +static int gup_hugepd(struct vm_area_struct *vma, hugepd_t hugepd, + unsigned long addr, unsigned int pdshift, + unsigned long end, unsigned int flags, + struct page **pages, int *nr) { pte_t *ptep; unsigned long sz = 1UL << hugepd_shift(hugepd); unsigned long next; + int ret; ptep = hugepte_offset(hugepd, addr, pdshift); do { next = hugepte_addr_end(addr, end, sz); - if (!gup_fast_hugepte(ptep, sz, addr, end, flags, pages, nr)) - return 0; + ret = gup_hugepte(vma, ptep, sz, addr, end, flags, pages, nr); + if (ret != 1) + return ret; } while (ptep++, addr = next, addr != end); return 1; @@ -613,22 +624,25 @@ static struct page *follow_hugepd(struct vm_area_struct *vma, hugepd_t hugepd, h = hstate_vma(vma); ptep = hugepte_offset(hugepd, addr, pdshift); ptl = huge_pte_lock(h, vma->vm_mm, ptep); - ret = gup_fast_hugepd(hugepd, addr, pdshift, addr + PAGE_SIZE, - flags, &page, &nr); + ret = gup_hugepd(vma, hugepd, addr, pdshift, addr + PAGE_SIZE, + flags, &page, &nr); spin_unlock(ptl); - if (ret) { + if (ret == 1) { + /* GUP succeeded */ WARN_ON_ONCE(nr != 1); ctx->page_mask = (1U << huge_page_order(h)) - 1; return page; } - return NULL; + /* ret can be either 0 (translates to NULL) or negative */ + return ERR_PTR(ret); } #else /* CONFIG_ARCH_HAS_HUGEPD */ -static inline int gup_fast_hugepd(hugepd_t hugepd, unsigned long addr, - unsigned int pdshift, unsigned long end, unsigned int flags, - struct page **pages, int *nr) +static inline int gup_hugepd(struct vm_area_struct *vma, hugepd_t hugepd, + unsigned long addr, unsigned int pdshift, + unsigned long end, unsigned int flags, + struct page **pages, int *nr) { return 0; } @@ -3261,8 +3275,8 @@ static int gup_fast_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, * architecture have different format for hugetlbfs * pmd format and THP pmd format */ - if (!gup_fast_hugepd(__hugepd(pmd_val(pmd)), addr, - PMD_SHIFT, next, flags, pages, nr)) + if (gup_hugepd(NULL, __hugepd(pmd_val(pmd)), addr, + PMD_SHIFT, next, flags, pages, nr) != 1) return 0; } else if (!gup_fast_pte_range(pmd, pmdp, addr, next, flags, pages, nr)) @@ -3291,8 +3305,8 @@ static int gup_fast_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, pages, nr)) return 0; } else if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) { - if (!gup_fast_hugepd(__hugepd(pud_val(pud)), addr, - PUD_SHIFT, next, flags, pages, nr)) + if (gup_hugepd(NULL, __hugepd(pud_val(pud)), addr, + PUD_SHIFT, next, flags, pages, nr) != 1) return 0; } else if (!gup_fast_pmd_range(pudp, pud, addr, next, flags, pages, nr)) @@ -3318,8 +3332,8 @@ static int gup_fast_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr, return 0; BUILD_BUG_ON(p4d_leaf(p4d)); if (unlikely(is_hugepd(__hugepd(p4d_val(p4d))))) { - if (!gup_fast_hugepd(__hugepd(p4d_val(p4d)), addr, - P4D_SHIFT, next, flags, pages, nr)) + if (gup_hugepd(NULL, __hugepd(p4d_val(p4d)), addr, + P4D_SHIFT, next, flags, pages, nr) != 1) return 0; } else if (!gup_fast_pud_range(p4dp, p4d, addr, next, flags, pages, nr)) @@ -3347,8 +3361,8 @@ static void gup_fast_pgd_range(unsigned long addr, unsigned long end, pages, nr)) return; } else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) { - if (!gup_fast_hugepd(__hugepd(pgd_val(pgd)), addr, - PGDIR_SHIFT, next, flags, pages, nr)) + if (gup_hugepd(NULL, __hugepd(pgd_val(pgd)), addr, + PGDIR_SHIFT, next, flags, pages, nr) != 1) return; } else if (!gup_fast_p4d_range(pgdp, pgd, addr, next, flags, pages, nr))