[v3,0/2] KVM: x86: Provide a capability to disable APERF/MPERF read intercepts

Message

Jim Mattson March 21, 2025, 10:14 p.m. UTC

Allow guest reads of IA32_APERF and IA32_MPERF, so that it can
determine the effective frequency multiplier for the physical LPU.

Commit b51700632e0e ("KVM: X86: Provide a capability to disable cstate
msr read intercepts") allowed the userspace VMM to grant a guest read
access to four core C-state residency MSRs. Do the same for IA32_APERF
and IA32_MPERF.

While this isn't sufficient to claim support for
CPUID.6:ECX.APERFMPERF[bit 0], it may suffice in a sufficiently
restricted environment (i.e. vCPUs pinned to LPUs, no TSC multiplier,
and no suspend/resume).

v1 -> v2: Add {IA32_APERF,IA32_MPERF} to vmx_possible_passthrough_msrs[]
v2 -> v3: Add a selftest

Jim Mattson (2):
  KVM: x86: Provide a capability to disable APERF/MPERF read intercepts
  KVM: selftests: Test behavior of KVM_X86_DISABLE_EXITS_APERFMPERF

 Documentation/virt/kvm/api.rst                |   1 +
 arch/x86/include/asm/kvm_host.h               |   1 +
 arch/x86/kvm/svm/svm.c                        |   7 +
 arch/x86/kvm/svm/svm.h                        |   2 +-
 arch/x86/kvm/vmx/vmx.c                        |   6 +
 arch/x86/kvm/vmx/vmx.h                        |   2 +-
 arch/x86/kvm/x86.c                            |   8 +-
 arch/x86/kvm/x86.h                            |   5 +
 include/uapi/linux/kvm.h                      |   1 +
 tools/include/uapi/linux/kvm.h                |   4 +-
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../selftests/kvm/x86/aperfmperf_test.c       | 162 ++++++++++++++++++
 12 files changed, 196 insertions(+), 4 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/x86/aperfmperf_test.c