From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 176C53B960C; Mon, 30 Mar 2026 10:11:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774865487; cv=none; b=qr81VcCVj/Lnpwwn8EBvIawCnkDMIaLfa/34AlwaJ2AEPpi9KyCYOGzFXywZjBCD22VekhQii1urgQirpEAcKqmC58SzHYQMdsHJ6i/amuVV4V27oBz+tWw2GsMqQEpoddLH6kUMaWBwKUA8LVbUBo8RGG6vuk/84/VGT7oosQg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774865487; c=relaxed/simple; bh=GgKA5DKfE0J6C86Pd58sBvtyWfrHRhL+cDnuFJprFXI=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=d7IN18xg93rrpr9g1uiDtmI7utWDtVKzSfyQcJ943/PnajGlKtRr0TaSvHa9fR0W1X6ohCYUq1jeUwFXXL9Qxty70DdumzOaBLXWRFNl36V/PYf6UQHYniUeEGqnqXAU9gBZ4MZzOeU5JL3O8Pj3xAyXbW7mD6OovTyBdjKuRUU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oz3RaLZ4; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="oz3RaLZ4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A05F4C2BCB1; Mon, 30 Mar 2026 10:11:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774865486; bh=GgKA5DKfE0J6C86Pd58sBvtyWfrHRhL+cDnuFJprFXI=; h=From:To:Cc:Subject:Date:From; b=oz3RaLZ4XqTIWA/YrlmEslKtMgjjzZUSf4/xnt5q9aPl5HExKWwVBg3skiD1JgDEc CF3Rpp229qlD1QYeyZo3hcEN6wHUVlMny1H+HiOqHCuZIj2lfzkQW4kCE8suuUFC9m +1lDQDpxmPbKzCEZw8l1FsNCAYq+fKRbyjBxu/NMgDFBYTMWx38HfNXla2kPCp4KcC 5sz3bn1qyjvp6w+/V7eKKJ1KCz+rrUybjpPdUM2kzPIAWQ9rVfx1uoI84wjSJ0mxFm 5FKaKj7HppkUc0triJODgpx/rn6uKvJgtF6w9bU+g9qiD1BkO8LoPN8fZxV8Vjob02 SUlzlK9XoqDnA== From: Mike Rapoport To: Andrew Morton Cc: Andrea Arcangeli , Andrei Vagin , Axel Rasmussen , Baolin Wang , David Hildenbrand , Harry Yoo , Hugh Dickins , James Houghton , "Liam R. Howlett" , "Lorenzo Stoakes (Oracle)" , "Matthew Wilcox (Oracle)" , Michal Hocko , Mike Rapoport , Muchun Song , Nikita Kalyazin , Oscar Salvador , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , kvm@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 00/15] mm, kvm: allow uffd support in guest_memfd Date: Mon, 30 Mar 2026 13:11:01 +0300 Message-ID: <20260330101116.1117699-1-rppt@kernel.org> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Mike Rapoport (Microsoft)" Hi, These patches enable support for userfaultfd in guest_memfd. As the ground work I refactored userfaultfd handling of PTE-based memory types (anonymous and shmem) and converted them to use vm_uffd_ops for allocating a folio or getting an existing folio from the page cache. shmem also implements callbacks that add a folio to the page cache after the data passed in UFFDIO_COPY was copied and remove the folio from the page cache if page table update fails. In order for guest_memfd to notify userspace about page faults, there are new VM_FAULT_UFFD_MINOR and VM_FAULT_UFFD_MISSING that a ->fault() handler can return to inform the page fault handler that it needs to call handle_userfault() to complete the fault. Nikita helped to plumb these new goodies into guest_memfd and provided basic tests to verify that guest_memfd works with userfaultfd. The handling of UFFDIO_MISSING in guest_memfd requires ability to remove a folio from page cache, the best way I could find was exporting filemap_remove_folio() to KVM. I deliberately left hugetlb out, at least for the most part. hugetlb handles acquisition of VMA and more importantly establishing of parent page table entry differently than PTE-based memory types. This is a different abstraction level than what vm_uffd_ops provides and people objected to exposing such low level APIs as a part of VMA operations. Also, to enable uffd in guest_memfd refactoring of hugetlb is not needed and I prefer to delay it until the dust settles after the changes in this set. v3 changes: * add fixes from Harry and Andrei * fix handling of WP-only mode for WP_ASYNC contexts in vma_can_userfault() * address David's comments about mfill_get_pmd() and rename it to mfill_establish_pmd() * add VM_WARN()s for unsupported operations (James) * update comments using James' suggestions v2: https://lore.kernel.org/all/20260306171815.3160826-1-rppt@kernel.org * instead of returning uffd-specific values from ->fault() handlers add __do_userfault() helper to resolve user faults in __do_fault() * address comments from Peter * rebased on v7.0-c1 RFC: https://lore.kernel.org/all/20260127192936.1250096-1-rppt@kernel.org Mike Rapoport (Microsoft) (11): userfaultfd: introduce mfill_copy_folio_locked() helper userfaultfd: introduce struct mfill_state userfaultfd: introduce mfill_establish_pmd() helper userfaultfd: introduce mfill_get_vma() and mfill_put_vma() userfaultfd: retry copying with locks dropped in mfill_atomic_pte_copy() userfaultfd: move vma_can_userfault out of line userfaultfd: introduce vm_uffd_ops shmem, userfaultfd: use a VMA callback to handle UFFDIO_CONTINUE userfaultfd: introduce vm_uffd_ops->alloc_folio() shmem, userfaultfd: implement shmem uffd operations using vm_uffd_ops userfaultfd: mfill_atomic(): remove retry logic Nikita Kalyazin (3): KVM: guest_memfd: implement userfaultfd operations KVM: selftests: test userfaultfd minor for guest_memfd KVM: selftests: test userfaultfd missing for guest_memfd Peter Xu (1): mm: generalize handling of userfaults in __do_fault() include/linux/mm.h | 5 + include/linux/shmem_fs.h | 14 - include/linux/userfaultfd_k.h | 73 +- mm/filemap.c | 1 + mm/hugetlb.c | 15 + mm/memory.c | 43 ++ mm/shmem.c | 188 ++--- mm/userfaultfd.c | 694 ++++++++++-------- .../testing/selftests/kvm/guest_memfd_test.c | 191 +++++ virt/kvm/guest_memfd.c | 84 ++- 10 files changed, 860 insertions(+), 448 deletions(-) base-commit: c369299895a591d96745d6492d4888259b004a9e -- 2.53.0