linux-kernel - Re: [PATCH v3 5/5] mips: use nth_page() in place of direct struct page manipulation.

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Date:   Wed, 13 Sep 2023 22:46:50 -0400
From:   Zi Yan <ziy@...dia.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org
Cc:     Zi Yan <ziy@...dia.com>, Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "\"Matthew Wilcox (Oracle)\"" <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        "\"Mike Rapoport (IBM)\"" <rppt@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH v3 5/5] mips: use nth_page() in place of direct struct
 page manipulation.

On 13 Sep 2023, at 16:12, Zi Yan wrote:

> From: Zi Yan <ziy@...dia.com>
>
> __flush_dcache_pages() is called during hugetlb migration via
> migrate_pages() -> migrate_hugetlbs() -> unmap_and_move_huge_page()
> -> move_to_new_folio() -> flush_dcache_folio(). And with hugetlb and
> without sparsemem vmemmap, struct page is not guaranteed to be contiguous
> beyond a section. Use nth_page() instead.
>
> Fixes: 15fa3e8e3269 ("mips: implement the new page table range API")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---
>  arch/mips/mm/cache.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/mips/mm/cache.c b/arch/mips/mm/cache.c
> index 02042100e267..7f830634dbe7 100644
> --- a/arch/mips/mm/cache.c
> +++ b/arch/mips/mm/cache.c
> @@ -117,7 +117,7 @@ void __flush_dcache_pages(struct page *page, unsigned int nr)
>  	 * get faulted into the tlb (and thus flushed) anyways.
>  	 */
>  	for (i = 0; i < nr; i++) {
> -		addr = (unsigned long)kmap_local_page(page + i);
> +		addr = (unsigned long)kmap_local_page(nth_page(page, i));
>  		flush_data_cache_page(addr);
>  		kunmap_local((void *)addr);
>  	}
> -- 
> 2.40.1

Without the fix, a wrong address might be used for data cache page flush.
No bug is reported. The fix comes from code inspection.


--
Best Regards,
Yan, Zi

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