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mm/gup: fix hugepd handling in hugetlb rework

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Commit a12083d721 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: a12083d721 ("mm/gup: handle hugepd for follow_page()")
Signed-off-by: Peter Xu <peterx@redhat.com>
Reported-by: David Hildenbrand <david@redhat.com>
Reviewed-by: David 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Peter Xu 2024-04-30 09:13:03 -04:00 committed by Andrew Morton
parent 67f4c91a44
commit 01d89b93e1
1 changed files with 39 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

64
mm/gup.c
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@ -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))