From: David Hildenbrand <david@redhat.com>
To: Lance Yang <lance.yang@linux.dev>,
akpm@linux-foundation.org, lorenzo.stoakes@oracle.com
Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com,
Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com,
dev.jain@arm.com, baohua@kernel.org, ioworker0@gmail.com,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Wei Yang <richard.weiyang@gmail.com>
Subject: Re: [PATCH mm-new v3 1/1] mm/khugepaged: guard is_zero_pfn() calls with pte_present()
Date: Mon, 20 Oct 2025 19:14:38 +0200 [thread overview]
Message-ID: <81fc5322-6ab4-4830-9b2e-15d834b461c2@redhat.com> (raw)
In-Reply-To: <20251020151111.53561-1-lance.yang@linux.dev>
On 20.10.25 17:11, Lance Yang wrote:
> From: Lance Yang <lance.yang@linux.dev>
>
> A non-present entry, like a swap PTE, contains completely different data
> (swap type and offset). pte_pfn() doesn't know this, so if we feed it a
> non-present entry, it will spit out a junk PFN.
>
> What if that junk PFN happens to match the zeropage's PFN by sheer
> chance? While really unlikely, this would be really bad if it did.
>
> So, let's fix this potential bug by ensuring all calls to is_zero_pfn()
> in khugepaged.c are properly guarded by a pte_present() check.
>
> Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Reviewed-by: Nico Pache <npache@redhat.com>
> Reviewed-by: Dev Jain <dev.jain@arm.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
> Signed-off-by: Lance Yang <lance.yang@linux.dev>
> ---
Works for me!
Acked-by: David Hildenbrand <david@redhat.com>
--
Cheers
David / dhildenb
next prev parent reply other threads:[~2025-10-20 17:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-20 15:11 Lance Yang
2025-10-20 17:14 ` David Hildenbrand [this message]
2025-10-20 17:46 ` Lorenzo Stoakes
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