linux-kernel - [PATCH v2 0/4] KVM ARM64 pre_fault

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Message-ID: <20251013151502.6679-1-jackabt.amazon@gmail.com>
Date: Mon, 13 Oct 2025 16:14:57 +0100
From: Jack Thomson <jackabt.amazon@...il.com>
To: maz@...nel.org,
	oliver.upton@...ux.dev,
	pbonzini@...hat.com
Cc: joey.gouly@....com,
	suzuki.poulose@....com,
	yuzenghui@...wei.com,
	catalin.marinas@....com,
	will@...nel.org,
	shuah@...nel.org,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	isaku.yamahata@...el.com,
	roypat@...zon.co.uk,
	kalyazin@...zon.co.uk,
	jackabt@...zon.com
Subject: [PATCH v2 0/4] KVM ARM64 pre_fault_memory

From: Jack Thomson <jackabt@...zon.com>

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 fixes an issue with unaligned mmap allocations
   in the selftests.

 - The third 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.

=== Changes Since v1 [2] ===

Addressing feedback from Oliver:

 - No pre-fault flag is passed to user_mem_abort() or gmem_abort() now
   aborts are synthesized.
 - Remove retry loop from kvm_arch_vcpu_pre_fault_memory()

[1]: https://lore.kernel.org/kvm/20240710174031.312055-1-pbonzini@redhat.com
[2]: https://lore.kernel.org/all/20250911134648.58945-1-jackabt.amazon@gmail.com

Jack Thomson (4):
  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

 Documentation/virt/kvm/api.rst                |   3 +-
 arch/arm64/kvm/Kconfig                        |   1 +
 arch/arm64/kvm/arm.c                          |   1 +
 arch/arm64/kvm/mmu.c                          |  73 +++++++++++-
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 tools/testing/selftests/kvm/lib/kvm_util.c    |  12 +-
 .../selftests/kvm/pre_fault_memory_test.c     | 110 +++++++++++++-----
 7 files changed, 163 insertions(+), 38 deletions(-)


base-commit: 42188667be387867d2bf763d028654cbad046f7b
-- 
2.43.0