[PATCH 0/5] KVM: x86/pmu: Hide guest counter updates from the VMRUN instruction

[Like Xu <like.xu.linux@gmail.com>]

Hi,

Considering that developers are more likely to have access to AMD VMs
and use vPMU inside guest, there's a dark cloud that needs to rain.
The x86_64/pmu_event_filter_test always fails on Zen3 boxes:

  test_amd_deny_list: Branch instructions retired = 43 (expected 42)
  test_without_filter: Branch instructions retired = 43 (expected 42)
  test_member_allow_list: Branch instructions retired = 43 (expected 42)
  test_not_member_deny_list: Branch instructions retired = 43 (expected 42)

,which is not caused by the event_filter feature (otherwise it's zero).

After some dubious guessing and microtesting on Zen3+ pmu hardware,
we found that VMRUN or one of the instructions in __svm_vcpu_run()
causes a guest-only enabled counter for counting guest instruction (in the
pmu_event_filter case, the branch instruction) to always increase by one
right after each vm_entry.

This creates an inconsistency with the AMD64_EVENTSEL_GUESTONLY,
where the vPMU user in the VM does not expect to see any counter
changes due to the SVM transaction at all. This patch set provides a low
overhead software fix until HW change arrives or simply no fix planned.

Prerequisite:
KVM: x86/pmu/misc: Fix a typo on kvm_pmu_request_counter_reprogam()
KVM: x86/pmu: Prevent the PMU from counting disallowed events

Please feel free to run more tests, add more or share comments.

Thanks,

Like Xu (5):
  KVM: x86/pmu: Emulate CTR overflow directly in kvm_pmu_handle_event()
  KVM: x86/pmu: Add a helper to check if pmc has PEBS mode enabled
  KVM: x86/pmu: Move the overflow of a normal counter out of PMI context
  KVM: x86/pmu: Reorder functions to reduce unnecessary declarations
  KVM: x86/pmu: Hide guest counter updates from the VMRUN instruction

 arch/x86/include/asm/kvm_host.h |  4 ++
 arch/x86/kvm/pmu.c              | 81 +++++++++++++++++++++------------
 arch/x86/kvm/pmu.h              | 37 +++++++++++++--
 arch/x86/kvm/svm/pmu.c          |  1 +
 arch/x86/kvm/svm/svm.c          | 28 ++++++++++++
 5 files changed, 119 insertions(+), 32 deletions(-)


base-commit: e79412ef245c53b2157458754327f39f43dd6a49
-- 
2.39.2