[PATCH 0/2] KVM: arm64: KVM: arm64: Add per-VM WFI/WFE exit disable capability

[David Woodhouse]

Add KVM_CAP_ARM_DISABLE_EXITS, modelled after the existing x86
KVM_CAP_X86_DISABLE_EXITS, to allow userspace to disable WFI and/or
WFE trapping on a per-VM basis.

KVM already has system-wide kernel command line parameters
(kvm-arm.wfi_trap_policy and kvm-arm.wfe_trap_policy, added in
0b5afe05377d) to control WFx trapping. However, these are global and
set at boot time. A per-VM capability allows the VMM to make the
decision per guest — for example, disabling WFI trapping for
latency-sensitive VMs with pinned vCPUs while keeping it enabled for
overcommitted guests on the same host.

When a flag is set via KVM_ENABLE_CAP, the corresponding trap is
unconditionally cleared, overriding the system-wide policy. When the
flag is not set, the system policy (including the default
single-task heuristic) applies as before.

As with the x86 equivalent, disabling exits is a one-way operation
per VM.

Tested on Graviton 3 (Neoverse-V1) metal.

David Woodhouse (2):
  KVM: arm64: Add KVM_CAP_ARM_DISABLE_EXITS for WFI/WFE passthrough
  KVM: arm64: selftests: Add KVM_CAP_ARM_DISABLE_EXITS UAPI test

 Documentation/virt/kvm/api.rst                    | 28 +++++++++++++
 arch/arm64/include/asm/kvm_host.h                 |  4 ++
 arch/arm64/kvm/arm.c                              | 20 ++++++++++
 include/uapi/linux/kvm.h                          |  6 +++
 tools/testing/selftests/kvm/Makefile.kvm          |  1 +
 tools/testing/selftests/kvm/arm64/disable_exits.c | 48 +++++++++++++++++++++++
 6 files changed, 107 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/arm64/disable_exits.c