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(p200300d82f239c00d1f6f7fe8f147e34.dip0.t-ipconnect.de. [2003:d8:2f23:9c00:d1f6:f7fe:8f14:7e34]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45df16070bdsm5517555e9.3.2025.09.09.02.07.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Sep 2025 02:07:37 -0700 (PDT) Message-ID: Date: Tue, 9 Sep 2025 11:07:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/7] mm: introduce local state for lazy_mmu sections To: Kevin Brodsky , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Alexander Gordeev , Andreas Larsson , Andrew Morton , Boris Ostrovsky , Borislav Petkov , Catalin Marinas , Christophe Leroy , Dave Hansen , "David S. Miller" , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Juergen Gross , "Liam R. Howlett" , Lorenzo Stoakes , Madhavan Srinivasan , Michael Ellerman , Michal Hocko , Mike Rapoport , Nicholas Piggin , Peter Zijlstra , Ryan Roberts , Suren Baghdasaryan , Thomas Gleixner , Vlastimil Babka , Will Deacon , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org References: <20250908073931.4159362-1-kevin.brodsky@arm.com> <20250908073931.4159362-3-kevin.brodsky@arm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250908073931.4159362-3-kevin.brodsky@arm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: tKqknDeveCRGbnnvl9eQZvraaK4Q9I8Y2GZUHKDQJAk_1757408859 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 36BD340005 X-Stat-Signature: fbhsdmsdzjnkpumken8rrdwkp4z5sy5x X-Rspam-User: X-HE-Tag: 1757408862-362649 X-HE-Meta: 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 ouHM95oE 77Ym52BAvr8/ZvXDxrYvtLKd2YdwEYoWtu0eR6nDiBXeNlIQkSOvPvduPDvMJ1HdNdBMhzlAAzpyBv4TP//7oM6cmCLmvDMEewk7Lo3Jtka2bdCmT92gEMG26f7hIXiMHEqDUOp8k7vyWwGBHDgl5zNuLdqr/PV6YucSOoSJSSOCcTzxMcfGIGtIY4syrtdXwzJIvxELco2sc9hDECEsPaeLfyB91FHYehlViFiBhn3N8+ZUbYOHQueL3+1EiWkv4VcVqrkweflttjRvWY3AwckSFRQkLqe+n/0sdhpIeMgtLzz/DueVsgGba6BLi57pt6UdAL2ElIrvrmYGOiCUEcWN+jqQI1Dg/4v2QPz28a5XcciqwBrakzQTmgL7FXskGcL6ViksXpkOoPQqaMa2dd9AGV2X5lz9Ws4MEFN8wauTzmLCEb8+3+tCoLCP2OoBZZpTCIgysWHRByZQ8zjWpLWP0nUvhQTsHL0Ya 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 08.09.25 09:39, Kevin Brodsky wrote: > arch_{enter,leave}_lazy_mmu_mode() currently have a stateless API > (taking and returning no value). This is proving problematic in > situations where leave() needs to restore some context back to its > original state (before enter() was called). In particular, this > makes it difficult to support the nesting of lazy_mmu sections - > leave() does not know whether the matching enter() call occurred > while lazy_mmu was already enabled, and whether to disable it or > not. > > This patch gives all architectures the chance to store local state > while inside a lazy_mmu section by making enter() return some value, > storing it in a local variable, and having leave() take that value. > That value is typed lazy_mmu_state_t - each architecture defining > __HAVE_ARCH_ENTER_LAZY_MMU_MODE is free to define it as it sees fit. > For now we define it as int everywhere, which is sufficient to > support nesting. > > The diff is unfortunately rather large as all the API changes need > to be done atomically. Main parts: > > * Changing the prototypes of arch_{enter,leave}_lazy_mmu_mode() > in generic and arch code, and introducing lazy_mmu_state_t. > > * Introducing LAZY_MMU_{DEFAULT,NESTED} for future support of > nesting. enter() always returns LAZY_MMU_DEFAULT for now. > (linux/mm_types.h is not the most natural location for defining > those constants, but there is no other obvious header that is > accessible where arch's implement the helpers.) > > * Changing all lazy_mmu sections to introduce a lazy_mmu_state > local variable, having enter() set it and leave() take it. Most of > these changes were generated using the following Coccinelle script: > > @@ > @@ > { > + lazy_mmu_state_t lazy_mmu_state; > ... > - arch_enter_lazy_mmu_mode(); > + lazy_mmu_state = arch_enter_lazy_mmu_mode(); > ... > - arch_leave_lazy_mmu_mode(); > + arch_leave_lazy_mmu_mode(lazy_mmu_state); > ... > } > > * In a few cases (e.g. xen_flush_lazy_mmu()), a function knows that > lazy_mmu is already enabled, and it temporarily disables it by > calling leave() and then enter() again. Here we want to ensure > that any operation between the leave() and enter() calls is > completed immediately; for that reason we pass LAZY_MMU_DEFAULT to > leave() to fully disable lazy_mmu. enter() will then re-enable it > - this achieves the expected behaviour, whether nesting occurred > before that function was called or not. > > Note: it is difficult to provide a default definition of > lazy_mmu_state_t for architectures implementing lazy_mmu, because > that definition would need to be available in > arch/x86/include/asm/paravirt_types.h and adding a new generic > #include there is very tricky due to the existing header soup. Yeah, I was wondering about exactly that. In particular because LAZY_MMU_DEFAULT etc resides somewehere compeltely different. Which raises the question: is using a new type really of any benefit here? Can't we just use an "enum lazy_mmu_state" and call it a day? -- Cheers David / dhildenb