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 A7EBC36AB5F; Fri, 6 Mar 2026 17:18:26 +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=1772817506; cv=none; b=oZQUjX6UWoCdWTqhdHlKdNr4ZUrNqyrFWHy4LRLAfGd0IctuttcKst/50QXMHIMNcULpFcAcqijITdBJ0bO3nSjKjMNDe2ndtJO75sdW38qfs62p+tUQftpeOMZVr80N1DZkvaOYsvCd4Werco7xAcdTvF9rkOmWM2r7hG/k5S4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772817506; c=relaxed/simple; bh=v65cD3N8Br5TyxfaG6Wxwe38me5rZ0c7uZMHqtZlcpM=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Y8s6mW7DRnQaY4nTEtXX5W+Ii97KprSTLYj9syJ9hyHjb1dGw0e05r3QfKtGKE3FGfFJ8U46PgzHZivhxoYuTcdn3SMCQMAWU/hEh0QjuqV9gQfhBLvSCYtdd5XXENgfLpPd0OjVNNQ+FC8RWJXVJPNIVvDQHS3t8K4FEtoqCDs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iyJNlXWY; 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="iyJNlXWY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7BA46C4CEF7; Fri, 6 Mar 2026 17:18:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772817506; bh=v65cD3N8Br5TyxfaG6Wxwe38me5rZ0c7uZMHqtZlcpM=; h=From:To:Cc:Subject:Date:From; b=iyJNlXWYG+bjR/gJhhrmzh9pBnw8sWL+QBOHdKQNMZ6rpLSb+yHZNoyQoTpLd08NP T714R3BgPR+lSW+R2gPVak0oKSXdaXOf+qvoLvUza23w6LW0j8/TRZAQM+LgY0oBQI Je+u50iWrjpTjKzBCHimbGNyMjofwuXW6pyc7U1w3tGzYba/F6eqwI6Q7r7F9sEEcR AR8U9wY6/xdShFjpFRBmdO5lBXMkhnLYIqyTtzARg+GqetrSO0RDItdFOXx/rS8SGu bxzY6rqPquiMavoVra2BfGwl9agSz1WpMuIr99Fz+d+HLby5uYJ80q59vUwA0FJCdK lKa031garTQdA== From: Mike Rapoport To: Andrew Morton Cc: Andrea Arcangeli , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , James Houghton , "Liam R. Howlett" , Lorenzo Stoakes , "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 v2 00/15] mm, kvm: allow uffd support in guest_memfd Date: Fri, 6 Mar 2026 19:18:00 +0200 Message-ID: <20260306171815.3160826-1-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-kselftest@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. v1 changes: * 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_get_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 | 692 ++++++++++-------- .../testing/selftests/kvm/guest_memfd_test.c | 191 +++++ virt/kvm/guest_memfd.c | 84 ++- 10 files changed, 858 insertions(+), 448 deletions(-) base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f -- 2.51.0