Re: [RESEND v13 09/10] KVM: vmx/pmu: Expose LBR_FMT in the MSR_IA32_PERF_CAPABILITIES

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On 27/01/21 06:45, Xu, Like wrote:
On 2021/1/26 17:30, Paolo Bonzini wrote:
On 08/01/21 02:37, Like Xu wrote:
Userspace could enable guest LBR feature when the exactly supported
LBR format value is initialized to the MSR_IA32_PERF_CAPABILITIES
and the LBR is also compatible with vPMU version and host cpu model.

Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
---
  arch/x86/kvm/vmx/capabilities.h | 9 ++++++++-
  arch/x86/kvm/vmx/vmx.c          | 7 +++++++
  2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index 57b940c613ab..a9a7c4d1b634 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -378,7 +378,14 @@ static inline u64 vmx_get_perf_capabilities(void)
       * Since counters are virtualized, KVM would support full
       * width counting unconditionally, even if the host lacks it.
       */
-    return PMU_CAP_FW_WRITES;
+    u64 perf_cap = PMU_CAP_FW_WRITES;
+
+    if (boot_cpu_has(X86_FEATURE_PDCM))
+        rdmsrl(MSR_IA32_PERF_CAPABILITIES, perf_cap);
+
+    perf_cap |= perf_cap & PMU_CAP_LBR_FMT;
+
+    return perf_cap;
  }
    static inline u64 vmx_supported_debugctl(void)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index ad3b079f6700..9cb5b1e4fc27 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2229,6 +2229,13 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
      case MSR_IA32_PERF_CAPABILITIES:
          if (data && !vcpu_to_pmu(vcpu)->version)
              return 1;
+        if (data & PMU_CAP_LBR_FMT) {
+            if ((data & PMU_CAP_LBR_FMT) !=
+                (vmx_get_perf_capabilities() & PMU_CAP_LBR_FMT))
+                return 1;
+            if (!intel_pmu_lbr_is_compatible(vcpu))
+                return 1;
+        }
          ret = kvm_set_msr_common(vcpu, msr_info);
          break;


Please move this hunk to patch 4.

Paolo

Thanks, I'll do this part early in the next version.

I would have thought that we need to
make the interface exposing as the last enabling step.

That's the right thing to do for vmx_get_perf_capabilities(). However, checking the values of MSR_IA32_PERF_CAPABILITIES can be done early.

Paolo




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