linux-kernel - [RFC PATCH 0/4] mm, kvm: add guest_memfd support for uffd minor faults

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251117114631.2029447-1-rppt@kernel.org>
Date: Mon, 17 Nov 2025 13:46:27 +0200
From: Mike Rapoport <rppt@...nel.org>
To: linux-mm@...ck.org
Cc: Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	David Hildenbrand <david@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Michal Hocko <mhocko@...e.com>,
	Mike Rapoport <rppt@...nel.org>,
	Nikita Kalyazin <kalyazin@...zon.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Peter Xu <peterx@...hat.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Shuah Khan <shuah@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: [RFC PATCH 0/4] mm, kvm: add guest_memfd support for uffd minor faults

From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>

Hi,

These patches allow guest_memfd to notify userspace about minor page
faults using userfaultfd and let userspace to resolve these page faults
using UFFDIO_CONTINUE.

To allow UFFDIO_CONTINUE outside of the core mm I added a
get_pagecache_folio() callback to vm_ops that allows an address space
backing a VMA to return a folio that exists in it's page cache (patch 2)

In order for guest_memfd to notify userspace about page faults, it has to
call handle_userfault() and since guest_memfd may be a part of kvm module,
handle_userfault() is exported for kvm module (patch 3).

Note that patch 3 changelog does not provide motivation for enabling uffd
in guest_memfd, mainly because I can't say I understand why is that
required :)
Would be great to hear from KVM folks about it.

This series is the minimal change I've been able to come up with to allow
integration of guest_memfd with uffd and while refactoring uffd and making
mfill_atomic() flow more linear would have been a nice improvement, it's
way out of the scope of enabling uffd with guest_memfd.

Mike Rapoport (Microsoft) (3):
  userfaultfd: move vma_can_userfault out of line
  userfaultfd, shmem: use a VMA callback to handle UFFDIO_CONTINUE
  userfaultfd, guest_memfd: support userfault minor mode in guest_memfd

Nikita Kalyazin (1):
  KVM: selftests: test userfaultfd minor for guest_memfd

 fs/userfaultfd.c                              |   4 +-
 include/linux/mm.h                            |   9 ++
 include/linux/userfaultfd_k.h                 |  36 +-----
 include/uapi/linux/userfaultfd.h              |   8 +-
 mm/shmem.c                                    |  20 ++++
 mm/userfaultfd.c                              |  88 ++++++++++++---
 .../testing/selftests/kvm/guest_memfd_test.c  | 103 ++++++++++++++++++
 virt/kvm/guest_memfd.c                        |  30 +++++
 8 files changed, 245 insertions(+), 53 deletions(-)


base-commit: 6146a0f1dfae5d37442a9ddcba012add260bceb0
-- 
2.50.1