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Thu, 05 Nov 2026 14:09:27 -0800 (PST) Received: from [192.168.1.22] ([83.231.69.9]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48fec8d8e29sm12845499f8f.19.2026.11.05.14.09.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Nov 2026 14:09:26 -0800 (PST) Message-ID: <9e98a961-fb45-4e61-a08b-d8d7f8e9894b@gmail.com> Date: Thu, 5 Nov 2026 23:09:24 +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 v2] x86/mm: Remove the zapped-entry checks To: Kiryl Shutsemau , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Rick Edgecombe , Andrew Morton , "David Hildenbrand (Arm)" Cc: "Kiryl Shutsemau (Meta)" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Peter Xu , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , "Mike Rapoport (Microsoft)" , Suren Baghdasaryan , Michal Hocko , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Pasha Tatashin , Andrew Donnellan , Rohan McLure , Tejun Heo , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20261105120322.3319301-1-kirill@shutemov.name> Content-Language: en-US From: "Jose A. Perez de Azpillaga" In-Reply-To: <20261105120322.3319301-1-kirill@shutemov.name> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/5/26 1:03 PM, Kiryl Shutsemau wrote: > From: "Kiryl Shutsemau (Meta)" > > Zapping a range calls arch_check_zapped_pte() for every batch of PTEs, > which is every page for small folios, and arch_check_zapped_pmd() or > arch_check_zapped_pud() for every huge leaf. Only x86 implements them, as > out-of-line functions that warn about a shadow stack entry (Write=0, > Dirty=1) in a VMA without VM_SHADOW_STACK. > > The warning is a VM_WARN_ON_ONCE(), so without CONFIG_DEBUG_VM the > functions are empty, but the calls remain. With the SRSO "Safe RET" > mitigation the return of every such call mispredicts. > > The x86 helpers already keep such entries out of other VMAs. > pte_wrprotect(), pte_mkdirty(), pte_modify() and their PMD versions go > through SavedDirty, and only pte_mkwrite() and pmd_mkwrite() on a > VM_SHADOW_STACK VMA create the combination. makes sense to me. Reviewed-by: Jose A. Perez de Azpillaga -- cheers, jose a. p-a