KVM: VMX: Give host userspace full control of MSR_IA32_PERF_CAPABILITIES

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Do not clear manipulate MSR_IA32_PERF_CAPABILITIES in intel_pmu_refresh(),
i.e. give userspace full control over capability/read-only MSRs.  KVM is
not a babysitter, it is userspace's responsiblity to provide a valid and
coherent vCPU model.

Attempting to "help" the guest by forcing a consistent model creates edge
cases, and ironicially leads to inconsistent behavior.

Example #1:  KVM doesn't do intel_pmu_refresh() when userspace writes
the MSR.

Example #2: KVM doesn't clear the bits when the PMU is disabled, or when
there's no architectural PMU.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220611005755.753273-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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Sean Christopherson 2022-06-11 00:57:50 +00:00 • committed by Paolo Bonzini

parent 9fc222967a

commit 0f4a718527

1 changed files with 0 additions and 2 deletions

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arch/x86/kvm/vmx/pmu_intel.c

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