[ based on kvm/next ]
Implement guest_memfd allocation and population via the write syscall.
This is useful in non-CoCo use cases where the host can access guest
memory. Even though the same can also be achieved via userspace mapping
and memcpying from userspace, write provides a more performant option
because it does not need to set page tables and it does not cause a page
fault for every page like memcpy would. Note that memcpy cannot be
accelerated via MADV_POPULATE_WRITE as it is not supported by
guest_memfd and relies on GUP.
Populating 512MiB of guest_memfd on a x86 machine:
- via memcpy: 436 ms
- via write: 202 ms (-54%)
v4:
- Switch from implementing the write callback to write_iter
- Remove conditional compilation
- Rebase to kvm/next
v3:
- https://lore.kernel.org/kvm/20250303130838.28812-1-kalyazin@amazon.com
- David/Mike D: Only compile support for the write syscall if
CONFIG_KVM_GMEM_SHARED_MEM (now gone) is enabled.
v2:
- https://lore.kernel.org/kvm/20241129123929.64790-1-kalyazin@amazon.com
- Switch from an ioctl to the write syscall to implement population
v1:
- https://lore.kernel.org/kvm/20241024095429.54052-1-kalyazin@amazon.com
Nikita Kalyazin (2):
KVM: guest_memfd: add generic population via write
KVM: selftests: update guest_memfd write tests
.../testing/selftests/kvm/guest_memfd_test.c | 85 +++++++++++++++++--
virt/kvm/guest_memfd.c | 64 +++++++++++++-
2 files changed, 142 insertions(+), 7 deletions(-)
base-commit: a6ad54137af92535cfe32e19e5f3bc1bb7dbd383
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2.50.1