From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A6653CD13DA for ; Tue, 5 May 2026 07:18:22 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id E968B10E99D; Tue, 5 May 2026 07:18:21 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.b="PSEuGZYl"; dkim-atps=neutral Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id 80A7C10E9A4 for ; Tue, 5 May 2026 07:18:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1777965500; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=U8Okzffkmp0X0il5ChdwD7WwCI7y675UlHMmtZ9sMKU=; b=PSEuGZYlHwpT8hLpSia8/GXY4GxsJNjQMH0/dd2Jna2bM2g2zR9QsucxdbN74K7w2H4pqS UIcq4IMXGxFCjg8eo/yR6w5mrfzA9nmSsWIp5LdPdHk09JCrv0nhcEgf/0xYx4SaIyObXq +NubJsIkL94Pkh1s9q6yACQPp81d6dY= Received: from mail-lf1-f72.google.com (mail-lf1-f72.google.com [209.85.167.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-607-Vye4wC1zMVmZ64MorJOH9A-1; Tue, 05 May 2026 03:18:17 -0400 X-MC-Unique: Vye4wC1zMVmZ64MorJOH9A-1 X-Mimecast-MFC-AGG-ID: Vye4wC1zMVmZ64MorJOH9A_1777965496 Received: by mail-lf1-f72.google.com with SMTP id 2adb3069b0e04-5a407fad7e0so2420404e87.0 for ; Tue, 05 May 2026 00:18:17 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1777965496; x=1778570296; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=U8Okzffkmp0X0il5ChdwD7WwCI7y675UlHMmtZ9sMKU=; b=D0z7sWBrRpYuott1MrzBYWbGmPTAEeiMO0GKGv6TCuW1KhDe5jdFQRgccRt1n2HpKG r9Zg3COmfWh9k4rzZb3IyEtOjk4UhP7nXAcTBrudJll9zh0QMkI8D+/z9szZZvDsFwMP 4Zz7d2sWsPBVir30zx14jUdBVBIQzJaMUVDTR33zeAE/iQp69hU3EKweHnwCUOwZZnPZ IyBO09Hs5DcbpFGk/fXaqafpcy533VL6OiD2fe8KwUvAGs4+BxqaXaRlM/8Lci0ojuuG Oce8C8m6vxLompwgylTyVZvDvmtkfIWfm+MPXZ2ae9uic02wguJxWseue+E5u8L157yN hf0Q== X-Forwarded-Encrypted: i=1; AFNElJ87vld67XrixNGB2/p1z2QEGlOw32oFqZ5d+yMI5YP2x71aX4X8rWq9cR6A0iGqdNivuFj50UOCJcc=@lists.freedesktop.org X-Gm-Message-State: AOJu0Yx+Unqbkodsvg0wMgW48C9l11Dir5kK3oWxEVhVKEs8iC+dHtxb DTJMVNcW1d+RqDIt35wGgQSYodN0lMCdbWjgE+ZtR5mdiR6vGH6lZaHJOSfKtH8vB9a5FOC0C8N 5h2rSdE5dxR82EhcJQ6FWNivtuknHmcladzigCpGVIoNqomlb1Kr/apA6IEMB3FMxwFdH X-Gm-Gg: AeBDieuv8f+MEsMNRFJ8dpfiQS0Vt9zvplMLbNYYh+Yzo6/686CYepu50qd6u7VMS/m vArx7tDnqIdFVhq5u1/cf80NGEl+bYGQiDveqbtK3+0rXq/mHul7nSt9/iKuGMiL35cakw47jqD cRKBUTxs2HwAXOx0vgDGDX+zhIEWfShBr+/DrHy4IDzqrqXlHdHRrTikN1sNi5XkEmrUkL949aB /+HHOdPQReNoeVbNPeKe2vi75oKswVb2WIrifh/nj9TCrgbyVjyzRfAE2HYUV2Fu+nOVZ3fuiD4 3h+vT+H5gyAPI3JKYieQia01mimUZHenZajMIm9T1Zbz2vNogvt3CdXO8l4KrLA+Txsgv9Az10R 3cv8v4eI/rfVRFkbTdHD5AWk8Nt68jmm/oDwA+WKlLT73LsK7woJadnLY9A== X-Received: by 2002:a05:6512:2527:b0:5a8:64cd:4d7d with SMTP id 2adb3069b0e04-5a864cd4d86mr4224308e87.37.1777965496062; Tue, 05 May 2026 00:18:16 -0700 (PDT) X-Received: by 2002:a05:6512:2527:b0:5a8:64cd:4d7d with SMTP id 2adb3069b0e04-5a864cd4d86mr4224268e87.37.1777965495404; Tue, 05 May 2026 00:18:15 -0700 (PDT) Received: from [192.168.1.86] (85-23-51-1.bb.dnainternet.fi. [85.23.51.1]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5a87791b4a2sm1029451e87.1.2026.05.05.00.18.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 May 2026 00:18:14 -0700 (PDT) Message-ID: Date: Tue, 5 May 2026 10:18:14 +0300 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 0/5] Migrate on fault for device pages To: Alistair Popple Cc: linux-mm@kvack.org, dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-kernel@vger.kernel.org, David Hildenbrand , Jason Gunthorpe , Leon Romanovsky , Balbir Singh , Zi Yan , Matthew Brost , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko References: <20260505051658.2219537-1-mpenttil@redhat.com> From: =?UTF-8?Q?Mika_Penttil=C3=A4?= In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: CzVMQgrDHWHWoBinuf6kq0dnkGDlyHFsZUOc8lL6EGQ_1777965496 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On 5/5/26 10:09, Alistair Popple wrote: > Thanks for doing this work Mika. I've been meaning to take a look at this series > for a while. I'm currently at LSFMM but will try and take a look this week or > next as it sounds quite useful. > > - Alistair Thanks Alistair and no problem, appreciate your insights whenever you have time. --Mika > > On 2026-05-05 at 15:16 +1000, mpenttil@redhat.com wrote... >> From: Mika Penttilä >> >> Currently, the way device page faulting and migration works >> is not optimal, if you want to do both fault handling and >> migration at once. >> >> Being able to migrate not present pages (or pages mapped with incorrect >> permissions, eg. COW) to the GPU requires doing either of the >> following sequences: >> >> 1. hmm_range_fault() - fault in non-present pages with correct permissions, etc. >> 2. migrate_vma_*() - migrate the pages >> >> Or: >> >> 1. migrate_vma_*() - migrate present pages >> 2. If non-present pages detected by migrate_vma_*(): >> a) call hmm_range_fault() to fault pages in >> b) call migrate_vma_*() again to migrate now present pages >> >> The problem with the first sequence is that you always have to do two >> page walks even when most of the time the pages are present or zero page >> mappings so the common case takes a performance hit. >> >> The second sequence is better for the common case, but far worse if >> pages aren't present because now you have to walk the page tables three >> times (once to find the page is not present, once so hmm_range_fault() >> can find a non-present page to fault in and once again to setup the >> migration). It is also tricky to code correctly. One page table walk >> could costs over 1000 cpu cycles on X86-64, which is a significant hit. >> >> We should be able to walk the page table once, faulting >> pages in as required and replacing them with migration entries if >> requested. >> >> Add a new flag to HMM APIs, HMM_PFN_REQ_MIGRATE, >> which tells to prepare for migration also during fault handling. >> Also, for the migrate_vma_setup() call paths, a flag, MIGRATE_VMA_FAULT, >> is added to tell to add fault handling to migrate. >> >> One extra benefit of migrating with hmm_range_fault() path >> is the migrate_vma.vma gets populated, so no need to >> retrieve that separataly. >> >> Tested in X86-64 VM with HMM test device, passing the selftests. >> For performance, the migrate throughput tests from the selftests >> show similar numbers (within error margin) as unmodified kernel. >> Tested also rebased on the >> "Remove device private pages from physical address space" series: >> https://lore.kernel.org/linux-mm/20260130111050.53670-1-jniethe@nvidia.com/ >> plus a small patch to adjust with no problems. >> >> Changes v8-v9 >> - rebase on drm-tip >> - fixed uaf around migrate_vma_split_folio() usage >> - added missing pmd unlock >> >> Changes v7-v8 >> - rebase on 7.0 >> - fixed subject in two patches >> - enhanced commit messages >> - squashed patch 6 into patch 4 to fix kernel test robot warning >> - readded dropped Cc block from cover letter >> - fixed white space >> >> Changes v6-v7 >> - rebase on 7.0.0-rc6 >> - added documentation and comments >> - denote to be migrated zero page as HMM_PFN_MIGRATE alone >> - got rid of HMM_PFN_INOUT_FLAGS movement in patch 2 >> - picked up Acked-By from David for patch 1 >> >> Changes v5-v6 >> - rebase on 7.0.0-rc4 >> - use range based TLB flushing while unmapping ptes >> - gate migration behind HMM_PFN_REQ_MIGRATE for fault and >> migrate paths >> - always infer migration flags from migrate->flags only >> >> Changes v4-v5 >> - rebase on 6.19 >> - fixed David's email address >> - fixed link issue without CONFIG_TRANSPARENT_HUGEPAGE >> - refactored into smaller commits >> - added more comments to code >> >> Changes v3-v4: >> - rebase on 6.19-rc8 >> - fixed issues found by kernel test robot with random configs >> - fixed typos >> >> Changes v2-v3: >> - rebase on 6.19-rc7 >> - fixed issues found by kernel test robot >> - fixed smatch issues reported by Dan Carpenter >> - fixes to lock handling (pmd/pte) on errors >> - added assertions for pmd/pte lock states >> - other issues discovered by Matthew, thanks! >> >> Changes v1-v2: >> - rebase on 6.19-rc6 >> - fixed issues found by kernel test robot >> - fixed locking (pmd/ptl) to cover handle_ and prepare_ regions >> parts if migrating >> - other issues discovered by Matthew, thanks! >> >> Changes RFC-v1: >> - rebase on 6.19-rc5 >> - adjust for the device THP >> - changes from feedback >> >> Revisions: >> - RFC https://lore.kernel.org/linux-mm/20250814072045.3637192-1-mpenttil@redhat.com/ >> - v1: https://lore.kernel.org/all/20260114091923.3950465-1-mpenttil@redhat.com/ >> - v2: https://lore.kernel.org/all/20260119112502.645059-1-mpenttil@redhat.com/ >> - v3: https://lore.kernel.org/all/20260126111939.1332983-2-mpenttil@redhat.com/ >> - v4: https://lore.kernel.org/all/20260202112622.2104213-1-mpenttil@redhat.com/ >> - v5: https://lore.kernel.org/linux-mm/20260211081301.2940672-1-mpenttil@redhat.com/ >> - v6: https://lore.kernel.org/linux-mm/20260316062407.3354636-1-mpenttil@redhat.com/ >> - v7: https://lore.kernel.org/linux-mm/20260330115611.347988-1-mpenttil@redhat.com/ >> - v8: https://lore.kernel.org/linux-mm/20260414041226.1539439-1-mpenttil@redhat.com/ >> >> Cc: David Hildenbrand >> Cc: Jason Gunthorpe >> Cc: Leon Romanovsky >> Cc: Alistair Popple >> Cc: Balbir Singh >> Cc: Zi Yan >> Cc: Matthew Brost >> Cc: Andrew Morton >> Cc: Lorenzo Stoakes >> Cc: "Liam R. Howlett" >> Cc: Vlastimil Babka >> Cc: Mike Rapoport >> Cc: Suren Baghdasaryan >> Cc: Michal Hocko >> >> Mika Penttilä (5): >> mm/Kconfig: changes for migrate on fault for device pages >> mm: Add helper to convert HMM pfn to migrate pfn >> mm/hmm: do the plumbing for HMM to participate in migration >> mm: setup device page migration in HMM pagewalk >> lib/test_hmm:: add a new testcase for the migrate on fault >> >> include/linux/hmm.h | 19 +- >> include/linux/migrate.h | 26 +- >> lib/test_hmm.c | 101 ++- >> lib/test_hmm_uapi.h | 19 +- >> mm/Kconfig | 2 + >> mm/hmm.c | 835 +++++++++++++++++++++++-- >> mm/migrate_device.c | 583 +++-------------- >> tools/testing/selftests/mm/hmm-tests.c | 54 ++ >> 8 files changed, 1066 insertions(+), 573 deletions(-) >> >> drm-tip >> base-commit: 94d56a898a2db27f841b17f6966a81ba502fe63c >> -- >> 2.50.0 >>