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Fri, 17 Oct 2025 16:10:07 +0800 Message-ID: Date: Fri, 17 Oct 2025 16:10:06 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-new 1/1] mm/khugepaged: guard is_zero_pfn() calls with pte_present() To: Lance Yang , akpm@linux-foundation.org, david@redhat.com, lorenzo.stoakes@oracle.com Cc: ziy@nvidia.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 References: <20251016033643.10848-1-lance.yang@linux.dev> From: Baolin Wang In-Reply-To: <20251016033643.10848-1-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Stat-Signature: imfj3urhscma6hefbz5iscn4r6o1u3kx X-Rspam-User: X-Rspamd-Queue-Id: D261F80005 X-HE-Tag: 1760688613-935164 X-HE-Meta: U2FsdGVkX19X59BuV340zcg88z3j5IWro5/n9S79DEImMI+5UtUqjJm89nS/s2fAmULSW/Sd1nQlGwh06qEZOUEWtGG23E2r34HqOVchtrfsIeuEu8FYYsxJ53r45XFI84Te8J2+g4qMfUmhvGNX94FhzIa0NMWfm8Ffk62u4ZB+VhN7RFtYnJ7s9K8J8wMH8NTykhDSPFCpBUFMA/LA86UHgPt3M6y1L8oiJjMBZy87CMdQVIGm51YAr0iW45oNyQwA23592rVjwOV/Eavf6ddMAxijf+3vM6WeMWpMi/2mUPWHJTgz9IBc5+KK/MvCLgTXCgDHveVo6/+lTD+UsPygkv7QcBufdkFUN0xtTalua77ZRNv72EuaUixY/FcvO/5NWOKQCdDufxhce4VF8yQuzrmxPTRxKJC1cASlgK8tvIZCTRrnSv142W/vAWvHz88dVacyOwknUHXzQX4HK72atOC9wqyY+RHuwO6h0zX6merO9SaS1yVM7782u1YiFzuYKhDVXWBwojeEXyd+gn73C+M1OBr8m+al1tS0TEartRDgxZ0LVsMRay3FSZEBX0UcTTS6TzcV0m4zydEYFs6fNJY5zWpkTS9i+BhnhltxF+IjFixerpDtZaVuHI5NNqKc8B9G6wsDqpy6P7dWk+V5CDrE/Egs5m6sL3mLfwnlvccY28zH1AppEJh45rYHyvtOmnkGZfbQ2MENKstHYxNYKpnT/LUeG4Riwu4tWrh2+y4fn+2OUbnCZx0yslBNuvuOlkg9wEU0NADIw7G2+uynmE37s7yp01GxxW7vGHPdPCxh84tD8fKo11NpeggugAt/X+T8p6ZcmQTg+YrXvX5J/a/gljPfgJHN0O1eg21H0wrS8GCMpCwZbo6NaFe25X2RFf9KcgZqFmxXEC+juYZ9sh+HKxHQKt5VLhhXe7BeurBuwWE9g6D5im0CzcexUCY0iFDUAgbhWurhRir 2BQGba2J Uw/npel0xvveJWrczhAJWEbhxgPCGelPlhpzyvNCBdUCGLaA0TGMYrfty4FRATnaYsYJGJNV5/SECuKEx73+Kt+drokRhn60l5qwT52ixvwRImWtLENEjUjOuwzVphuNggi6+a+L+5I206jMhqsSFi+xYwF+xI4xe5leJ+SIUoT0AccDhP7sl07WeD9SuXh80O06N6IR92K6C8vKF2kx1HGFCZpqETjL1dden/5AXgevGfeiPMFLt7oWPjxXg6ViNRd/8+xJ4qv6pPM9N4hXnCRTfK1ffTnCQFwTAtK/r8ylt83AetzvTwpl1qyCE6pT6z3mN/pPi8k1cA8YjiOgO1EfhCQsoyWrRMBm28KJY/6DudYtns8SmOTOAwQ== 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 2025/10/16 11:36, 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. > > Suggested-by: Lorenzo Stoakes > Signed-off-by: Lance Yang > --- LGTM. Reviewed-by: Baolin Wang