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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> 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) X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 9D35F180008 X-Stat-Signature: ifyf14fkqaucagks3pmhtw13jxsaojwp X-Rspam-User: X-HE-Tag: 1760607193-430276 X-HE-Meta: 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 knFyaCKb GCox838k61b6SPjc7Gq5hl14J8Lb8vSD/M79wjpVxFLwTLCOP1L5DwfA1RIwO9+73G1KO3NkAKZvTJlgziN2SXN//MaWVkKpLvgEkHefEiFjU0OpEo7stiDD5DNP17Aa24iV7wkZq3I+GnEu/kfwvY9WOW3lcXG/kmuJVLw2y7oYDVLAG7+HhWmSZXS1/8yZ9VNliDlvQ7X44tDV1xqbynkGVN77YDqyljLysu8FLglyXZMU/yzU/HR/xYeEKPcSWX+O5uQmGCTkqDZjJn11vC4Yo3vh2fLkvtk47XntwxOWI8XsOTKnTrZ/duXRbIvrzNeyyDFBybBk6gWlIU1h2zG5n8YupGUh0QylXdG9HxGs5N7F9A5u15U08CHP1gzd0C2TGrBb8X9yBZcRKRrkaRv+YAWz8Us2N8n2DX9n6C2rmbMUp69JfQk2AnTkVw/SWsCgegoNyTc79+aT1LTvkfQQfVoTIM1iidR84LvGcbh+XvfIQTrMsVfaNFbJMAG6KGn74PJdKJyqlYLurdj7Mc1zpTnw3yshFkcu0XE0xBk7U1FUNde1hIgmv6uViisGWTz6JI+bd8Y7gGfOqUzhveU3EPeIE4DB+onlUtcvscNGMjsRNY/8R/uF7NXrl87jdXXfUrXsNqKOoeTfYl+XMGTUcXXQdRAflte4Aygz1oGG+JgcRVruYS2nKQA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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