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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, Mark Rutland References: <20250908073931.4159362-1-kevin.brodsky@arm.com> <20250908073931.4159362-3-kevin.brodsky@arm.com> <2fecfae7-1140-4a23-a352-9fd339fcbae5-agordeev@linux.ibm.com> <47ee1df7-1602-4200-af94-475f84ca8d80@arm.com> <29383ee2-d6d6-4435-9052-d75a263a5c45@redhat.com> <9de08024-adfc-421b-8799-62653468cf63@arm.com> <4b4971fd-0445-4d86-8f3a-6ba3d68d15b7@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: <4b4971fd-0445-4d86-8f3a-6ba3d68d15b7@arm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 39sFvdb5DT85-gcTkbLMh1AXUAu8X1T4VuPplPwcw18_1757614449 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: qegama4p8txjh5rjdrzkoczh7rwkfgo4 X-Rspam-User: X-Rspamd-Queue-Id: 7F8081C000D X-Rspamd-Server: rspam04 X-HE-Tag: 1757614454-660082 X-HE-Meta: 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 fe/1K38t T2uTTsPT5RNqKEVLQoW7MtLutO6GcpvjFoBguSVfFgJLAgmX9dqYDwTgz4F4jwptst9+YgxDmg9Q/NhAgSirU4qRL8eJYEvvmav7YKL1xelwBG7+61JSZqCBOWaD6wLSRLH6jRLPjVr+FBoW7cXsDhrRR7nmmlvT9wKo50XqVzEnbnu94pcRYrLbiq0fzk7qTf3SPD2s3U7nbFDwYhzIdPPCtZcQtIB+OptuU+9JxYmZovDjAI8arf1QlKeQ2xMNVL8ge7qFpHZaDA/yV38PsxSi026dNaMhbDBnTkTeDactfOfEWA/XZnWZdaQjO1iVREEzkrud7bJo0n/oWHtGdC0YqjBM/qDWuWBN/iaL2pJvIEjQBl8fKKPnb7qvCJosHc1VfjoVV0LwCrPk6pDPAl3blMYvtyu0kMmmYqutEFr0u/iGlWJsZ3Cl0SbjRFj6lxmN8O6nFRPUWgWYI97/wqAc4utIUysz5Frwx 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 the other hand, with a pagefault_disabled-like approach, there is no >>> way to instruct call {3} to fully exit lazy_mmu regardless of the >>> nesting level. >> >> Sure there is, with a better API. See below. :) > > I meant while keeping the existing shape of the API but yes fair enough! Time to do it properly I guess :) [...] >> Assume we store in the task_struct >> >> uint8_t lazy_mmu_enabled_count; >> bool lazy_mmu_paused; > > I didn't think of that approach! I can't immediately see any problem > with it, assuming we're fine with storing arch-specific context in > thread_struct (which seems to be the case as things stand). Right, just to complete the picture: a) We will have some CONFIG_ARCH_LAZY_MMU b) Without that config, all lazy_mmu_*() functions are a nop and no lazy_mmu_state is stored in task_struct struct lazy_mmu_state { uint8_t enabled_count; bool paused; } c) With that config, common-code lazy_mmu_*() functions implement the updating of the lazy_mmu_state in task_struct and call into arch code on the transition from 0->1, 1->0 etc. Maybe that can be done through exiting arch_enter_lazy_mmu_mode()/arch_leave_lazy_mmu_mode() callbacks, maybe we need more. I feel like we might be able to implement that through the existing helpers. > >> >> We can do things like >> >> a) Sanity check that while we are paused that we get no more >> enable/disable requests >> b) Sanity check that while we are paused that we get no more pause >> requests. > > These are good points - and this is only possible with such global > state. (Similarly we can check that the counter never underflows.) Exactly. [..] > > Overall what you're proposing seems sensible to me, the additional > fields in task_struct don't take much space and we can keep the API > unchanged in most cases. It is also good to have the option to check > that the API is used correctly. I'll reply to the cover letter to let > anyone who didn't follow this thread chip in, before I go ahead and try > out that new approach. And on top of the proposal above we will have some struct arch_lazy_mmu_state; define by the architecture (could be an empty struct on most). We can store that inside "struct lazy_mmu_state;" or if we ever have to, start returning only that from the enable/disable etc. functions. For now, I'd say just store it in the task struct in the lazy_mmu_state. But we can always adjust later if required. In the first (this) series we probably don't even have to introduce arch_lazy_mmu_state. -- Cheers David / dhildenb