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

Like Xu
2023-03-10T10:54:29Z

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
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2.39.2