From: Sean Christopherson seanjc@google.com
commit 145dfad998eac74abc59219d936e905766ba2d98 upstream.
Advertise LBR support to userspace via MSR_IA32_PERF_CAPABILITIES if and only if perf fully supports LBRs. Perf may disable LBRs (by zeroing the number of LBRs) even on platforms the allegedly support LBRs, e.g. if probing any LBR MSRs during setup fails.
Fixes: be635e34c284 ("KVM: vmx/pmu: Expose LBR_FMT in the MSR_IA32_PERF_CAPABILITIES") Reported-by: Like Xu like.xu.linux@gmail.com Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20221006000314.73240-3-seanjc@google.com Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/vmx/capabilities.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/arch/x86/kvm/vmx/capabilities.h +++ b/arch/x86/kvm/vmx/capabilities.h @@ -404,6 +404,7 @@ static inline bool vmx_pebs_supported(vo static inline u64 vmx_get_perf_capabilities(void) { u64 perf_cap = PMU_CAP_FW_WRITES; + struct x86_pmu_lbr lbr; u64 host_perf_cap = 0;
if (!enable_pmu) @@ -412,7 +413,8 @@ static inline u64 vmx_get_perf_capabilit if (boot_cpu_has(X86_FEATURE_PDCM)) rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
- perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT; + if (x86_perf_get_lbr(&lbr) >= 0 && lbr.nr) + perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
if (vmx_pebs_supported()) { perf_cap |= host_perf_cap & PERF_CAP_PEBS_MASK;