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    Subject[PATCH 07/75] mm/gup: Fix some contiguous memmap assumptions
    Date
    Several functions in gup.c assume that a compound page has virtually
    contiguous page structs. This isn't true for SPARSEMEM configs unless
    SPARSEMEM_VMEMMAP is also set. Fix them by using nth_page() instead of
    plain pointer arithmetic.

    Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Reviewed-by: John Hubbard <jhubbard@nvidia.com>
    Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
    Reviewed-by: William Kucharski <william.kucharski@oracle.com>
    ---
    mm/gup.c | 14 +++++++-------
    1 file changed, 7 insertions(+), 7 deletions(-)

    diff --git a/mm/gup.c b/mm/gup.c
    index 7e4bdae83e9b..29a8021f10a2 100644
    --- a/mm/gup.c
    +++ b/mm/gup.c
    @@ -260,7 +260,7 @@ static inline struct page *compound_range_next(struct page *start,
    struct page *next, *page;
    unsigned int nr = 1;

    - next = start + i;
    + next = nth_page(start, i);
    page = compound_head(next);
    if (PageHead(page))
    nr = min_t(unsigned int,
    @@ -2462,8 +2462,8 @@ static int record_subpages(struct page *page, unsigned long addr,
    {
    int nr;

    - for (nr = 0; addr != end; addr += PAGE_SIZE)
    - pages[nr++] = page++;
    + for (nr = 0; addr != end; nr++, addr += PAGE_SIZE)
    + pages[nr] = nth_page(page, nr);

    return nr;
    }
    @@ -2498,7 +2498,7 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
    VM_BUG_ON(!pfn_valid(pte_pfn(pte)));

    head = pte_page(pte);
    - page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
    + page = nth_page(head, (addr & (sz - 1)) >> PAGE_SHIFT);
    refs = record_subpages(page, addr, end, pages + *nr);

    head = try_grab_compound_head(head, refs, flags);
    @@ -2558,7 +2558,7 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
    pages, nr);
    }

    - page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
    + page = nth_page(pmd_page(orig), (addr & ~PMD_MASK) >> PAGE_SHIFT);
    refs = record_subpages(page, addr, end, pages + *nr);

    head = try_grab_compound_head(pmd_page(orig), refs, flags);
    @@ -2592,7 +2592,7 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
    pages, nr);
    }

    - page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
    + page = nth_page(pud_page(orig), (addr & ~PUD_MASK) >> PAGE_SHIFT);
    refs = record_subpages(page, addr, end, pages + *nr);

    head = try_grab_compound_head(pud_page(orig), refs, flags);
    @@ -2621,7 +2621,7 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,

    BUILD_BUG_ON(pgd_devmap(orig));

    - page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
    + page = nth_page(pgd_page(orig), (addr & ~PGDIR_MASK) >> PAGE_SHIFT);
    refs = record_subpages(page, addr, end, pages + *nr);

    head = try_grab_compound_head(pgd_page(orig), refs, flags);
    --
    2.34.1
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