From: Jack Thomson <jackabt@amazon.com>

Overview:

This patch series adds ARM64 support for the KVM_PRE_FAULT_MEMORY
feature, which was previously only available on x86 [1]. This allows
a reduction in the number of stage-2 faults during execution. This is
beneficial in post-copy migration scenarios, particularly in memory
intensive applications, where high latencies are experienced due to
the stage-2 faults when pre-populating memory via UFFD / memcpy.

Patch Overview:

 - The first patch is a preparatory refactor.

 - The second patch is adding a page walk flag for pre-faulting.

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

 - The fourth patch fixes an issue with unaligned mmap allocations
   in the selftests.

 - The fifth 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.

[1]: https://lore.kernel.org/kvm/20240710174031.312055-1-pbonzini@redhat.com

Jack Thomson (6):
  KVM: arm64: Add __gmem_abort and __user_mem_abort
  KVM: arm64: Add KVM_PGTABLE_WALK_PRE_FAULT walk flag
  KVM: arm64: Add pre_fault_memory implementation
  KVM: selftests: Fix unaligned mmap allocations
  KVM: selftests: Enable pre_fault_memory_test for arm64
  KVM: selftests: Add option for different backing in pre-fault tests

 arch/arm64/include/asm/kvm_pgtable.h          |   3 +
 arch/arm64/kvm/Kconfig                        |   1 +
 arch/arm64/kvm/arm.c                          |   1 +
 arch/arm64/kvm/hyp/pgtable.c                  |   6 +-
 arch/arm64/kvm/mmu.c                          |  97 +++++++++++++--
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 tools/testing/selftests/kvm/lib/kvm_util.c    |  12 +-
 .../selftests/kvm/pre_fault_memory_test.c     | 110 +++++++++++++-----
 8 files changed, 186 insertions(+), 45 deletions(-)


base-commit: 42188667be387867d2bf763d028654cbad046f7b
-- 
2.43.0

Hi Jack,

On Thu, Sep 11, 2025 at 02:46:42PM +0100, Jack Thomson wrote:
> From: Jack Thomson <jackabt@amazon.com>
> 
> Overview:
> 
> This patch series adds ARM64 support for the KVM_PRE_FAULT_MEMORY
> feature, which was previously only available on x86 [1]. This allows
> a reduction in the number of stage-2 faults during execution. This is
> beneficial in post-copy migration scenarios, particularly in memory
> intensive applications, where high latencies are experienced due to
> the stage-2 faults when pre-populating memory via UFFD / memcpy.

Thanks for posting the series. More of a general comment on the UAPI
documentation:

  "... However, KVM does not mark any newly created stage-2 PTE as Accessed."

This behavior is x86-specific since kvm_pgtable_stage2_map() will lay
down PTEs with the AF set. Probably shouldn't have documented the
internal state of the stage-2 in the first place but oh well, please
just update the UAPI description to make it clear this is x86-specific.

Thanks
Oliver