From: Sean Christopherson <seanjc@google.com>
To: Ackerley Tng <ackerleytng@google.com>
Cc: Mike Rapoport <rppt@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Andrei Vagin <avagin@google.com>,
Axel Rasmussen <axelrasmussen@google.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
David Hildenbrand <david@kernel.org>,
Harry Yoo <harry.yoo@oracle.com>, Hugh Dickins <hughd@google.com>,
James Houghton <jthoughton@google.com>,
"Liam R. Howlett" <Liam.Howlett@oracle.com>,
"Lorenzo Stoakes (Oracle)" <ljs@kernel.org>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
Michal Hocko <mhocko@suse.com>,
Muchun Song <muchun.song@linux.dev>,
Nikita Kalyazin <kalyazin@amazon.com>,
Oscar Salvador <osalvador@suse.de>,
Paolo Bonzini <pbonzini@redhat.com>, Peter Xu <peterx@redhat.com>,
Shuah Khan <shuah@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Vlastimil Babka <vbabka@suse.cz>,
kvm@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-mm@kvack.org, tarunsahu@google.com
Subject: Re: [PATCH v4 13/15] KVM: guest_memfd: implement userfaultfd operations
Date: Mon, 18 May 2026 13:42:41 -0700 [thread overview]
Message-ID: <agt5wTK5I-FvlB57@google.com> (raw)
In-Reply-To: <CAEvNRgHd4azPaMddvqnSG+Z5fmg+LWd+pz=LSB3PrJTW618dww@mail.gmail.com>
On Fri, May 15, 2026, Ackerley Tng wrote:
> Sean Christopherson <seanjc@google.com> writes:
>
> >
> > [...snip...]
> >
> >> +#ifdef CONFIG_USERFAULTFD
> >> +static bool kvm_gmem_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags)
> >> +{
> >> + struct inode *inode = file_inode(vma->vm_file);
> >> +
> >> + /*
> >> + * Only support userfaultfd for guest_memfd with INIT_SHARED flag.
> >> + * This ensures the memory can be mapped to userspace.
> >> + */
>
> Is the principle here that any memory that is allowed to be mapped to
> userspace can be userfault-ed?
Yes? It's more the opposite though: memory that can't be SHARED and thus can't
be mapped into userspace can't possibly support userfaultfd. Six of one, half
dozen of the other, but I think it's important to highlight that there's no
judgment call being made, i.e. we aren't deciding to support only SHARED just
because we're lazy, it's a hard requirement.
next prev parent reply other threads:[~2026-05-18 20:42 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-02 4:11 [PATCH v4 00/15] mm, kvm: allow uffd support in guest_memfd Mike Rapoport
2026-04-02 4:11 ` [PATCH v4 01/15] userfaultfd: introduce mfill_copy_folio_locked() helper Mike Rapoport
2026-04-02 4:11 ` [PATCH v4 02/15] userfaultfd: introduce struct mfill_state Mike Rapoport
2026-04-03 11:19 ` Harry Yoo (Oracle)
2026-04-02 4:11 ` [PATCH v4 03/15] userfaultfd: introduce mfill_establish_pmd() helper Mike Rapoport
2026-04-02 4:11 ` [PATCH v4 04/15] userfaultfd: introduce mfill_get_vma() and mfill_put_vma() Mike Rapoport
2026-04-03 12:54 ` Harry Yoo (Oracle)
2026-04-02 4:11 ` [PATCH v4 05/15] userfaultfd: retry copying with locks dropped in mfill_atomic_pte_copy() Mike Rapoport
2026-04-06 1:54 ` Harry Yoo (Oracle)
2026-04-02 4:11 ` [PATCH v4 06/15] userfaultfd: move vma_can_userfault out of line Mike Rapoport
2026-04-02 4:11 ` [PATCH v4 07/15] userfaultfd: introduce vm_uffd_ops Mike Rapoport
2026-04-02 19:32 ` Tal Zussman
2026-04-09 17:18 ` Mike Rapoport
2026-04-02 4:11 ` [PATCH v4 08/15] shmem, userfaultfd: use a VMA callback to handle UFFDIO_CONTINUE Mike Rapoport
2026-04-02 4:11 ` [PATCH v4 09/15] userfaultfd: introduce vm_uffd_ops->alloc_folio() Mike Rapoport
2026-04-02 4:11 ` [PATCH v4 10/15] shmem, userfaultfd: implement shmem uffd operations using vm_uffd_ops Mike Rapoport
2026-04-02 4:11 ` [PATCH v4 11/15] userfaultfd: mfill_atomic(): remove retry logic Mike Rapoport
2026-04-02 13:47 ` Mike Rapoport
2026-04-02 18:23 ` Andrew Morton
2026-04-02 4:11 ` [PATCH v4 12/15] mm: generalize handling of userfaults in __do_fault() Mike Rapoport
2026-04-02 4:11 ` [PATCH v4 13/15] KVM: guest_memfd: implement userfaultfd operations Mike Rapoport
2026-04-02 22:05 ` Sean Christopherson
2026-04-07 15:01 ` Nikita Kalyazin
2026-04-09 11:50 ` Mike Rapoport
2026-05-15 18:34 ` Ackerley Tng
2026-05-18 20:42 ` Sean Christopherson [this message]
2026-05-19 18:56 ` Ackerley Tng
2026-04-02 4:11 ` [PATCH v4 14/15] KVM: selftests: test userfaultfd minor for guest_memfd Mike Rapoport
2026-04-02 4:11 ` [PATCH v4 15/15] KVM: selftests: test userfaultfd missing " Mike Rapoport
2026-04-02 4:35 ` [PATCH v4 00/15] mm, kvm: allow uffd support in guest_memfd Andrew Morton
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