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  1. Jun 17, 2024
  3. May 16, 2024
    • Elliot Berman's avatar
      mm/gup: Introduce exclusive GUP pinning · f2c887da
      Elliot Berman authored 
      In arm64 pKVM and QuIC's Gunyah protected VM model, we want to support
grabbing shmem user pages instead of using KVM's guestmemfd. When these
pages are lent to a guest and made inaccessible to Linux, we need to
ensure that the kernel doesn't try to access these pages: a fault occurs
otherwise. To do this, we need to ensure that no page pins exist prior
to lending the page to the guest.  Previously discussed in a PUCK
session and in [1], we introduce the concept of "exclusive GUP pinning",
which enforces that only one GUP pin is allowed when the flag is set.
When FOLL_EXCLUSIVE is set, that corresponding pin ensures that no other
pins have been made and sets a bias in the refcount that ensures no
future pins (FOLL_EXCLUSIVE or otherwise) are allowed. This behavior
doesn't affect FOLL_GET or any other folio refcount operations that
don't go through the FOLL_PIN path.

[1]: https://lore.kernel.org/all/20240319143119.GA2736@willie-the-truck/



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To: Andrew Morton <akpm@linux-foundation.org>
To: Shuah Khan <shuah@kernel.org>
To: David Hildenbrand <david@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
To: maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, seanjc@google.com, Vishal Annapurve <vannapurve@google.com>, Fuad Tabba <tabba@google.com>
Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev
Cc: linux-arm-msm@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
Signed-off-by: default avatarElliot Berman <quic_eberman@quicinc.com>

--- b4-submit-tracking ---
# This section is used internally by b4 prep for tracking purposes.
{
  "series": {
    "revision": 1,
    "change-id": "20240509-exclusive-gup-66259138bbff",
    "prefixes": [
      "RFC"
    ]
  }
}
      f2c887da
  5. May 11, 2024
  7. May 07, 2024