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Thu, 16 Oct 2025 02:33:11 -0700 (PDT) Date: Thu, 16 Oct 2025 09:33:10 +0000 From: Wei Yang To: Lance Yang Cc: akpm@linux-foundation.org, david@redhat.com, lorenzo.stoakes@oracle.com, 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 Subject: Re: [PATCH mm-new 1/1] mm/khugepaged: guard is_zero_pfn() calls with pte_present() Message-ID: <20251016093310.rilvenglgnr65ojq@master> Reply-To: Wei Yang References: <20251016033643.10848-1-lance.yang@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251016033643.10848-1-lance.yang@linux.dev> User-Agent: NeoMutt/20170113 (1.7.2) On Thu, Oct 16, 2025 at 11:36:43AM +0800, Lance Yang wrote: >From: Lance Yang > >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. > Does it more like to guard pte_pfn() with pte_present()? -- Wei Yang Help you, Help me