linux-kernel - Re: [PATCH v2 06/28] gup: Fix some contiguous memmap assumptions

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Message-ID: <f4954822-16f9-3239-539e-ac7549700577@nvidia.com>
Date:   Mon, 10 Jan 2022 17:47:29 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>, linux-mm@...ck.org
Cc:     Christoph Hellwig <hch@...radead.org>,
        William Kucharski <william.kucharski@...cle.com>,
        linux-kernel@...r.kernel.org, Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH v2 06/28] gup: Fix some contiguous memmap assumptions

On 1/9/22 20:23, Matthew Wilcox (Oracle) wrote:
> 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@...radead.org>
> ---
>   mm/gup.c | 14 +++++++-------
>   1 file changed, 7 insertions(+), 7 deletions(-)

Reviewed-by: John Hubbard <jhubbard@...dia.com>

thanks,
-- 
John Hubbard
NVIDIA

> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 8a0ea220ced1..9c0a702a4e03 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -235,7 +235,7 @@ static inline struct page *compound_range_next(unsigned long i,
>   	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,
> @@ -2430,8 +2430,8 @@ 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;
>   }
> @@ -2466,7 +2466,7 @@ 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);
> @@ -2526,7 +2526,7 @@ 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);
> @@ -2560,7 +2560,7 @@ 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);
> @@ -2589,7 +2589,7 @@ 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);