KVM: VMX: Ignore guest CPUID for host userspace writes to DEBUGCTL
Ignore guest CPUID for host userspace writes to the DEBUGCTL MSR, KVM's ABI is that setting CPUID vs. state can be done in any order, i.e. KVM allows userspace to stuff MSRs prior to setting the guest's CPUID that makes the new MSR "legal". Keep the vmx_get_perf_capabilities() check for guest writes, even though it's technically unnecessary since the vCPU's PERF_CAPABILITIES is consulted when refreshing LBR support. A future patch will clean up vmx_get_perf_capabilities() to avoid the RDMSR on every call, at which point the paranoia will incur no meaningful overhead. Note, prior to vmx_get_perf_capabilities() checking that the host fully supports LBRs via x86_perf_get_lbr(), KVM effectively relied on intel_pmu_lbr_is_enabled() to guard against host userspace enabling LBRs on platforms without full support. Fixes: c6462363 ("KVM: vmx/pmu: Add PMU_CAP_LBR_FMT check when guest LBR is enabled") Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20221006000314.73240-5-seanjc@google.com> Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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