Commit 01d89b93 authored by Peter Xu's avatar Peter Xu Committed by Andrew Morton
Browse files

mm/gup: fix hugepd handling in hugetlb rework 

Commit a12083d7 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: a12083d7 ("mm/gup: handle hugepd for follow_page()")
Signed-off-by: default avatarPeter Xu <peterx@redhat.com>
Reported-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 67f4c91a

mm/gup.c

+39 −25
Original line number Diff line number Diff line
@@ -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,

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;
@@ -613,21 +624,24 @@ 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,

	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,

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))