[PATCH v4 0/3] KVM ARM64 pre_fault_memory

Jack Thomson
2026-01-13T15:27:32Z

This patch series adds ARM64 support for the KVM_PRE_FAULT_MEMORY
feature, which was previously only available on x86 [1]. This allows us
to reduce the number of stage-2 faults during execution. This is of
benefit in post-copy migration scenarios, particularly in memory
intensive applications, where we are experiencing high latencies due to
the stage-2 faults.

Patch Overview:

- The first patch adds support for the KVM_PRE_FAULT_MEMORY ioctl
on arm64.

- The second patch updates the pre_fault_memory_test to support
arm64.

- The last patch extends the pre_fault_memory_test to cover
different vm memory backings.

With regards to the additional parameter to `user_mem_abort`, noted in
the v3 review, would you like this to be fixed in this series or would
a follow-up series be ok? I also found a series from Sean which looks
to address this [2].

=== Changes Since v3 [3] ===

- Updated to now return -EOPNOTSUPP for pKVM. Previously this was not
checked.
- When running a nested guest, properly resolve the L2 IPA to L1 IPA
before pre faulting.
- Refactoring, page_size is now unsigned and ordered definitions at
top of pre_fault function.

Thanks Marc for your review

=== Changes Since v2 [4] ===

- Update fault info synthesize value. Thanks Suzuki
- Remove change to selftests for unaligned mmap allocations. Thanks
Sean

[1]: https://lore.kernel.org/kvm/20240710174031.312055-1-pbonzini@redhat.com
[2]: https://lore.kernel.org/linux-arm-kernel/20250821210042.3451147-1-seanjc@google.com/
[3]: https://lore.kernel.org/linux-arm-kernel/20251119154910.97716-1-jackabt.amazon@gmail.com
[4]: https://lore.kernel.org/linux-arm-kernel/20251013151502.6679-1-jackabt.amazon@gmail.com

Jack Thomson (3):
KVM: arm64: Add pre_fault_memory implementation
KVM: selftests: Enable pre_fault_memory_test for arm64
KVM: selftests: Add option for different backing in pre-fault tests

Documentation/virt/kvm/api.rst | 3 +-
arch/arm64/kvm/Kconfig | 1 +
arch/arm64/kvm/arm.c | 1 +
arch/arm64/kvm/mmu.c | 79 +++++++++++-
tools/testing/selftests/kvm/Makefile.kvm | 1 +
.../selftests/kvm/pre_fault_memory_test.c | 115 ++++++++++++++----
6 files changed, 169 insertions(+), 31 deletions(-)

base-commit: 3611ca7c12b740e250d83f8bbe3554b740c503b0
--
2.43.0