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[83.60.147.6]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-498362eb158sm11708192f8f.36.2026.11.11.08.54.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 Nov 2026 08:54:21 -0800 (PST) Message-ID: <6a2c3f50-bce4-4214-8621-e0daa0637e91@gmail.com> Date: Wed, 11 Nov 2026 17:54:19 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/4] mm/huge_memory: don't warn when a page table blocks a huge pfn insert To: Eliav Farber , Andrew Morton Cc: David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , x86@kernel.org, William Kucharski , Vishal Moola , Alex Williamson , Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261111140655.34281-1-farbere@amazon.com> <20261111140655.34281-4-farbere@amazon.com> Content-Language: en-US From: "Jose A. Perez de Azpillaga" In-Reply-To: <20261111140655.34281-4-farbere@amazon.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/11/26 3:06 PM, Eliav Farber wrote: > insert_pmd() and insert_pud() treat a non-empty entry at their own level > as a leaf and compare its PFN against the one being inserted. A page > table installed by a concurrent order-0 fault also makes the entry > non-empty, and pmd_pfn()/pud_pfn() then report the PFN of that table, > which never matches. insert_pmd() warns unless the entry is the huge > zero PMD, and insert_pud() warns on any mismatch. > > A VM_PFNMAP mapping with both ->fault and ->huge_fault can produce the > mixed orders: an order-0 fault installs a page table over an address > while a concurrent huge fault on the same address reaches insert_pmd(). > Changing an mm's THP policy while another thread faults the same PMD, > for example with prctl(PR_SET_THP_DISABLE), is enough to do it. > > Compare the PFN only for a leaf entry. A page table is not an error, so > take the existing out_unlock path, which returns VM_FAULT_NOPAGE and > lets the access refault onto the smaller entry. > > Fixes: f9e54c3a2f5b ("vfio/pci: implement huge_fault support") > Signed-off-by: Eliav Farber LGTM: Reviewed-by: Jose A. Perez de Azpillaga -- cheers, jose a. p-a