From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7D06244C51A; Fri, 24 Jul 2026 19:00:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784919667; cv=none; b=PP0+61NkkTK6+1Xa3CBwW0WufN+0SReKxGlZBhJ1uRAeKIrpFljI1wD4e6hiqX2i6k+dcg+gbbLYRF8i9DFDUsePrTTMyZ18mFLqDjiXpWOwUOZGslOG87M5UcVlr816E/luAp7YGc1seTRYIekoNbd78wR2IjLrGJPeHsm30bo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784919667; c=relaxed/simple; bh=mFwIVUdQtJOXDow4H9Nj5Z64tVHIjqkth2Fy54HgvFc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=H807Krcf+MJ+ySEZQ95A2lzUTR2HlpPB7HegxJrIvnI4ArWQ1wk00UdI/j4vT/kVZeGRVuFPD8ejJVZGPH9A4C9mOUu9Aiy4QiODCe8qDudBbgrAbwTSLy08cYfkFxT1Y5nKhv8IPV9EA5tq7ltg3GVMCj1QmZpzTVWT3l000I8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BySPDMLU; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="BySPDMLU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 978A21F000E9; Fri, 24 Jul 2026 19:00:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784919636; bh=t/DUzw2XQL2VWs73JF/hBihkxhoiKQkVH9v4AAAkPbI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=BySPDMLUedTvFGRdY+q6sY5P40LHYi/KfYHWFxuW9N0D9mj4H/mlNHZJVOWlR1/p+ rk1X1AM0CdVOtPPO9W2THyVVLk3WKJZiPTzi60gZfswKiJbaMq+vD3Z8YSnURusXIG sKuyYxi/svOx7URz5YRNX+w+wtcAQ7hfJIM0hAybzvpoQDYPzhW0di3qOHASv22by7 e93dJyd8YnhDYPvay5xBlWlD/x4+P2ulvqVLT/WmLaFHzBN8fnN5i1PXzJHe5gBraB 381Kn7NmIcSEIjSO0hdvZ3rmECO6r3S1PPeJKItdYdqommPu39Z7AXgQyvkJ2lrm6+ DftE3CxOyiI/A== Message-ID: <7655eaad-dcbf-4275-93f6-1f92ffedfa76@kernel.org> Date: Fri, 24 Jul 2026 21:00:24 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 1/8] mm/hmm: move page fault handling out of walk callbacks To: Stanislav Kinsburskii , Jason Gunthorpe , Leon Romanovsky , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Shuah Khan , Shuah Khan , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Lyude Paul , Danilo Krummrich , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Min Ma , Lizhi Hou , Oded Gabbay Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-hyperv@vger.kernel.org, dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, linux-rdma@vger.kernel.org References: <20260723-hmm-v10-v11-0-c55b003a4b61@gmail.com> <20260723-hmm-v10-v11-1-c55b003a4b61@gmail.com> 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: <20260723-hmm-v10-v11-1-c55b003a4b61@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/23/26 19:36, Stanislav Kinsburskii wrote: > hmm_range_fault() currently triggers page faults from inside the page-table > walk callbacks: hmm_vma_walk_pmd(), hmm_vma_walk_pud(), > hmm_vma_walk_hugetlb_entry() and the pte-level helper all call > hmm_vma_fault(), which in turn calls handle_mm_fault() while the walker > still holds nested locks. The pte spinlock is dropped explicitly by each > caller, and the hugetlb path manually drops and retakes > hugetlb_vma_lock_read around the fault to dodge a deadlock against the walk > framework's unconditional unlock. > > This layering does not extend cleanly to fault handlers that may release > mmap_lock (VM_FAULT_RETRY, VM_FAULT_COMPLETED). If the lock is dropped > while walk_page_range() is mid-traversal, the VMA can be freed before the > walk framework's matching hugetlb_vma_unlock_read(), turning that unlock > into a use-after-free. > > Split the responsibilities the way get_user_pages() does. Walk callbacks > become inspect-only: when they detect a range that needs to be faulted in, > they record it in struct hmm_vma_walk and return a private sentinel > (HMM_FAULT_PENDING). The outer loop in hmm_range_fault() then drops out of > walk_page_range(), invokes a new helper hmm_do_fault() that calls > handle_mm_fault() with only mmap_lock held, and restarts the walk so the > now-present entries are collected into hmm_pfns. > > No functional change for existing callers. As a side effect the hugetlb > callback no longer needs the hugetlb_vma_{un}lock_read dance, and every > fault-path exit from the callbacks now releases the pte spinlock on a > single, common path. This refactor is also a precursor for adding an > unlockable variant of hmm_range_fault() in a follow-up patch. > > Reviewed-by: Jason Gunthorpe > Signed-off-by: Stanislav Kinsburskii > --- Any reason my RB got dropped? https://lore.kernel.org/all/0b9be5b3-93aa-407f-b83d-409bec4b55e1@kernel.org/ -- Cheers, David