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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 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 Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 3D6D1180003 X-Stat-Signature: 6kinhbitg7fcqb8qia5eqqjhernq1qjb X-Rspam-User: X-HE-Tag: 1749561862-312301 X-HE-Meta: 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 +1Hq8fr5 OOiQZ7HQnMTwMf5DIYTs8LdhedQU3syJPZ2ri7Wef4gVsiVVP611ouJ0jOXXnhzCXIWO5y0bPCib/USr6dZjwQpSQlfXaQBku0CfPb4XCbTs5fF13oxxJ/ke/z+PNd00uhF1OGzmZ1K1ZbjTiQRIq/kkruPYeLoiAjimUBy1tud3/8NroIYLv5uKetdrFHLsCF790A1kWqrk5oGoJLrU2N8S/Mazx1By0Sjo7FIf66wPrpgiwUWbQFiNZuScTL7E8DDt5JKSVXJTerzg5/cAt3ZBC+NgTAtD72MAqrpUEbaQKv8RWZbwOQScRiexSbh69TZSaeGgoSRIpzJ5RrLZ1DxIotnMky/EPV7irZl2yRaDqLHPYJbKK0Dcr+2X7z4yWCsMNJgJBV5G6yRYhBuwkqde+y58c291o6Ux68tyW9/qSpr/Zq/feq5EuMf2yeDWtjNSncvF5umKKBJ6DvfwTN5n1QQ== 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 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