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b=A+6BW5OPP6fq/QKr9cgbG4pDUJxtSVWOEP2jOYcgkXDRXC2M6VOrRTy0xdXOH5tc6 DZXet3mOOqFZ3TTXsM4k3brhMAd33l0+ACPzw0ETx4EDl5Yd9M4Nk1XjkwyoMizldD muQqzHi3Mf5fbvq/Gy7m2Idm3tPgObuzN1km3ZSZkh7rW24eYdLSX41e+IAHkwRnG7 g/I/DrpgHad3VVIO3LWlyIJ0hy4UefQ/88lxbEphdhMSKYCoWYhGixnXRO+XmaVC5H KpBTWfcA9NIUxVJmYnU84LnD4K+KUFY9p2AxuhRW2vGQZTcS7V4oqeP3caEZoLMHt8 SxRZrFIdRVj2A== Message-ID: <665a19a0-47c2-404c-bd2b-482ab51b8f64@kernel.org> Date: Tue, 31 Mar 2026 23:11:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/2] mm: make lazy MMU mode context-aware To: Alexander Gordeev Cc: Kevin Brodsky , Andrew Morton , Gerald Schaefer , Heiko Carstens , Christian Borntraeger , Vasily Gorbik , linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <44dd86c0-1845-4dd9-b4b4-2cef6d1c6357@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 0D43740014 X-Stat-Signature: 1p1z5gm476npq7juzw1e17hogjsmp7cw X-Rspam-User: X-HE-Tag: 1774991487-747634 X-HE-Meta: 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/25/26 17:20, Alexander Gordeev wrote: > On Wed, Mar 25, 2026 at 10:55:23AM +0100, David Hildenbrand (Arm) wrote: > > Hi David, > >>> +/** >>> + * lazy_mmu_mode_enable_pte() - Enable the lazy MMU mode with parameters >> >> You have to be a lot clearer about implications. For example, what >> happens if we would bail out and not process all ptes? What are the >> exact semantics. > > The only implication is "only this address/PTE range could be updated > and that range may span one page table at most". Probably phrase it stronger. "No ptes outside of this range must be updated" etc. > > Whether all or portion of PTEs were actually updated is not defined, > just like in case of lazy_mmu_mode_enable_pte(). Okay, then let's document that. > > Makes sense? > Yes. >>> + * Enters a new lazy MMU mode section; if the mode was not already enabled, >>> + * enables it and calls arch_enter_lazy_mmu_mode_pte(). >>> + * >>> + * Must be paired with a call to lazy_mmu_mode_disable(). >>> + * >>> + * Has no effect if called: >>> + * - While paused - see lazy_mmu_mode_pause() >>> + * - In interrupt context >>> + */ >>> +static inline void lazy_mmu_mode_enable_pte(struct mm_struct *mm, >>> + unsigned long addr, >>> + unsigned long end, >>> + pte_t *ptep) >> >> It can be multiple ptes, so should this be some kind of "pte_range"/ >> >> lazy_mmu_mode_enable_for_pte_range() >> >> A bit mouthful but clearer. >> >>> +{ >>> + struct lazy_mmu_state *state = ¤t->lazy_mmu_state; >>> + >>> + if (in_interrupt() || state->pause_count > 0) >>> + return; >>> + >>> + VM_WARN_ON_ONCE(state->enable_count == U8_MAX); >>> + >>> + if (state->enable_count++ == 0) >>> + arch_enter_lazy_mmu_mode_pte(mm, addr, end, ptep); > > I will also change arch_enter_lazy_mmu_mode_pte() to > arch_enter_lazy_mmu_mode_for_pte_range() then. > >>> +} >> >> I'm wondering whether that could instead be some optional interface that >> we trigger after the lazy_mmu_mode_enable. But looking at > > To me just two separate and (as you put it) mouthful names appeal better > than an optional follow-up interface. Yes, probably better. -- Cheers, David