Re: [PATCH v3 1/5] mm/cma: use nth_page() in place of direct struct page manipulation.

From: Zi Yan <ziy@nvidia.com>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	linux-mips@vger.kernel.org
Cc: Zi Yan <ziy@nvidia.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	"\"Matthew Wilcox (Oracle)\"" <willy@infradead.org>,
	David Hildenbrand <david@redhat.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Muchun Song <muchun.song@linux.dev>,
	"\"Mike Rapoport (IBM)\"" <rppt@kernel.org>,
	stable@vger.kernel.org, Muchun Song <songmuchun@bytedance.com>
Subject: Re: [PATCH v3 1/5] mm/cma: use nth_page() in place of direct struct page manipulation.
Date: Wed, 13 Sep 2023 22:16:45 -0400	[thread overview]
Message-ID: <5C626EBA-B115-4A95-8D55-5EE28C872419@nvidia.com> (raw)
In-Reply-To: <20230913201248.452081-2-zi.yan@sent.com>

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

> From: Zi Yan <ziy@nvidia.com>
>
> When dealing with hugetlb pages, manipulating struct page pointers
> directly can get to wrong struct page, since struct page is not guaranteed
> to be contiguous on SPARSEMEM without VMEMMAP. Use nth_page() to handle
> it properly.
>
> Fixes: 2813b9c02962 ("kasan, mm, arm64: tag non slab memory allocated via pagealloc")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  mm/cma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/cma.c b/mm/cma.c
> index da2967c6a223..2b2494fd6b59 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -505,7 +505,7 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
>  	 */
>  	if (page) {
>  		for (i = 0; i < count; i++)
> -			page_kasan_tag_reset(page + i);
> +			page_kasan_tag_reset(nth_page(page, i));
>  	}
>
>  	if (ret && !no_warn) {
> -- 
> 2.40.1

Without the fix, page_kasan_tag_reset() could reset wrong page tags, causing
a wrong kasan result. No related bug is reported. The fix comes from code
inspection.

--
Best Regards,
Yan, Zi

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