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Mon, 07 Nov 2022 11:17:49 -0500 X-MC-Unique: izDZkPSsPkGvihn_mMeNNw-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A911185A59D; Mon, 7 Nov 2022 16:17:47 +0000 (UTC) Received: from t480s.redhat.com (unknown [10.39.195.106]) by smtp.corp.redhat.com (Postfix) with ESMTP id E6FEE4B3FC8; Mon, 7 Nov 2022 16:17:41 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, etnaviv@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, linux-kselftest@vger.kernel.org, David Hildenbrand , Linus Torvalds , Andrew Morton , Jason Gunthorpe , John Hubbard , Peter Xu , Greg Kroah-Hartman , Andrea Arcangeli , Hugh Dickins , Nadav Amit , Vlastimil Babka , Matthew Wilcox , Mike Kravetz , Muchun Song , Lucas Stach , David Airlie , Oded Gabbay , Arnd Bergmann Subject: [PATCH RFC 00/19] mm/gup: remove FOLL_FORCE usage from drivers (reliable R/O long-term pinning) Date: Mon, 7 Nov 2022 17:17:21 +0100 Message-Id: <20221107161740.144456-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 ARC-Authentication-Results: i=1; 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dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Hg8cyVb3; spf=pass (imf28.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam05 X-Rspam-User: X-HE-Tag: 1667837880-784610 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: For now, we did not support reliable R/O long-term pinning in COW mappings. That means, if we would trigger R/O long-term pinning in MAP_PRIVATE mapping, we could end up pinning the (R/O-mapped) shared zeropage or a pagecache page. The next write access would trigger a write fault and replace the pinned page by an exclusive anonymous page in the process page table; whatever the process would write to that private page copy would not be visible by the owner of the previous page pin: for example, RDMA could read stale data. The end result is essentially an unexpected and hard-to-debug memory corruption. Some drivers tried working around that limitation by using "FOLL_FORCE|FOLL_WRITE|FOLL_LONGTERM" for R/O long-term pinning for now. FOLL_WRITE would trigger a write fault, if required, and break COW before pinning the page. FOLL_FORCE is required because the VMA might lack write permissions, and drivers wanted to make that working as well, just like one would expect (no write access, but still triggering a write access to break COW). However, that is not a practical solution, because (1) Drivers that don't stick to that undocumented and debatable pattern would still run into that issue. For example, VFIO only uses FOLL_LONGTERM for R/O long-term pinning. (2) Using FOLL_WRITE just to work around a COW mapping + page pinning limitation is unintuitive. FOLL_WRITE would, for example, mark the page softdirty or trigger uffd-wp, even though, there actually isn't going to be any write access. (3) The purpose of FOLL_FORCE is debug access, not access without lack of VMA permissions by arbitrarty drivers. So instead, make R/O long-term pinning work as expected, by breaking COW in a COW mapping early, such that we can remove any FOLL_FORCE usage from drivers. More details in patch #8. Patches #1--#3 add COW tests for non-anonymous pages. Patches #4--#7 prepare core MM for extended FAULT_FLAG_UNSHARE support in COW mappings. Patch #8 implements reliable R/O long-term pinning in COW mappings Patches #9--#19 remove any FOLL_FORCE usage from drivers. I'm refraining from CCing all driver maintainers on the whole patch set. Cc: Linus Torvalds Cc: Andrew Morton Cc: Jason Gunthorpe Cc: John Hubbard Cc: Peter Xu Cc: Greg Kroah-Hartman Cc: Andrea Arcangeli Cc: Hugh Dickins Cc: Nadav Amit Cc: Vlastimil Babka Cc: Matthew Wilcox (Oracle) Cc: Mike Kravetz Cc: Muchun Song Cc: Shuah Khan Cc: David Airlie Cc: Oded Gabbay Cc: Arnd Bergmann David Hildenbrand (19): selftests/vm: anon_cow: prepare for non-anonymous COW tests selftests/vm: cow: basic COW tests for non-anonymous pages selftests/vm: cow: R/O long-term pinning reliability tests for non-anon pages mm: add early FAULT_FLAG_UNSHARE consistency checks mm: add early FAULT_FLAG_WRITE consistency checks mm: rework handling in do_wp_page() based on private vs. shared mappings mm: don't call vm_ops->huge_fault() in wp_huge_pmd()/wp_huge_pud() for private mappings mm: extend FAULT_FLAG_UNSHARE support to anything in a COW mapping mm/gup: reliable R/O long-term pinning in COW mappings RDMA/umem: remove FOLL_FORCE usage RDMA/usnic: remove FOLL_FORCE usage RDMA/siw: remove FOLL_FORCE usage media: videobuf-dma-sg: remove FOLL_FORCE usage drm/etnaviv: remove FOLL_FORCE usage media: pci/ivtv: remove FOLL_FORCE usage mm/frame-vector: remove FOLL_FORCE usage drm/exynos: remove FOLL_FORCE usage RDMA/hw/qib/qib_user_pages: remove FOLL_FORCE usage habanalabs: remove FOLL_FORCE usage drivers/gpu/drm/etnaviv/etnaviv_gem.c | 8 +- drivers/gpu/drm/exynos/exynos_drm_g2d.c | 2 +- drivers/infiniband/core/umem.c | 8 +- drivers/infiniband/hw/qib/qib_user_pages.c | 2 +- drivers/infiniband/hw/usnic/usnic_uiom.c | 9 +- drivers/infiniband/sw/siw/siw_mem.c | 9 +- drivers/media/common/videobuf2/frame_vector.c | 2 +- drivers/media/pci/ivtv/ivtv-udma.c | 2 +- drivers/media/pci/ivtv/ivtv-yuv.c | 5 +- drivers/media/v4l2-core/videobuf-dma-sg.c | 14 +- drivers/misc/habanalabs/common/memory.c | 3 +- include/linux/mm.h | 27 +- include/linux/mm_types.h | 8 +- mm/gup.c | 10 +- mm/huge_memory.c | 5 +- mm/hugetlb.c | 12 +- mm/memory.c | 97 +++-- tools/testing/selftests/vm/.gitignore | 2 +- tools/testing/selftests/vm/Makefile | 10 +- tools/testing/selftests/vm/check_config.sh | 4 +- .../selftests/vm/{anon_cow.c => cow.c} | 387 +++++++++++++++++- tools/testing/selftests/vm/run_vmtests.sh | 8 +- 22 files changed, 516 insertions(+), 118 deletions(-) rename tools/testing/selftests/vm/{anon_cow.c => cow.c} (74%)