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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a53244f516sm12244725f8f.74.2025.06.10.06.24.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Jun 2025 06:24:17 -0700 (PDT) Message-ID: <970e1b84-7f47-4a51-ad99-4df9026b8f7d@redhat.com> Date: Tue, 10 Jun 2025 15:24:16 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] mm: Allow lockless kernel pagetable walking To: Lorenzo Stoakes , Dev Jain Cc: akpm@linux-foundation.org, catalin.marinas@arm.com, will@kernel.org, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, suzuki.poulose@arm.com, steven.price@arm.com, gshan@redhat.com, linux-arm-kernel@lists.infradead.org, yang@os.amperecomputing.com, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20250610114401.7097-1-dev.jain@arm.com> <20250610114401.7097-2-dev.jain@arm.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10.06.25 14:07, Lorenzo Stoakes wrote: > OK so I think the best solution here is to just update check_ops_valid(), which > was kind of sucky anyway (we check everywhere but walk_page_range_mm() to > enforce the install pte thing). > > Let's do something like: > > #define OPS_MAY_INSTALL_PTE (1<<0) > #define OPS_MAY_AVOID_LOCK (1<<1) > > and update check_ops_valid() to take a flags or maybe 'capabilities' field. > > Then check based on this e.g.: > > if (ops->install_pte && !(capabilities & OPS_MAY_INSTALL_PTE)) > return false; > > if (ops->walk_lock == PGWALK_NOLOCK && !(capabilities & OPS_MAY_AVOID_LOCK)) > return false; > Hm. I mean, we really only want to allow this lockless check for walk_kernel_page_table_range(), right? Having a walk_kernel_page_table_range_lockeless() might (or might not) be better, to really only special-case this specific path. So, I am wondering if we should further start splitting the kernel-page-table walker up from the mm walker, at least on the "entry" function for now. -- Cheers, David / dhildenb