On 28/1/2023 8:14 am, Sean Christopherson wrote:
Disallow enabling LBR support if the CPU supports architectural LBRs.
Traditional LBR support is absent on CPU models that have architectural
LBRs, and KVM doesn't yet support arch LBRs, i.e. KVM will pass through
non-existent MSRs if userspace enables LBRs for the guest.
True, we have call_trace due to MSR_ARCH_LBR_FROM_0 (0x1500) for example.
Cc: stable@xxxxxxxxxxxxxxx
Cc: Yang Weijiang <weijiang.yang@xxxxxxxxx>
Cc: Like Xu <like.xu.linux@xxxxxxxxx>
Tested-by: Like Xu <likexu@xxxxxxxxxxx>
Reported-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Fixes: 145dfad998ea ("KVM: VMX: Advertise PMU LBRs if and only if perf supports
LBRs")
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
Am I missing something that would prevent this scenario?
arch/x86/kvm/vmx/vmx.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 8f0f67c75f35..77ee6b4a5ec4 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7761,9 +7761,11 @@ static u64 vmx_get_perf_capabilities(void)
if (boot_cpu_has(X86_FEATURE_PDCM))
rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
- x86_perf_get_lbr(&lbr);
- if (lbr.nr)
- perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
+ if (!cpu_feature_enabled(X86_FEATURE_ARCH_LBR)) {
To avoid changing this again in the Arch lbr enabling part, how about:
x86_perf_get_lbr(&lbr);
if (lbr.nr && cpu_feature_enabled(X86_FEATURE_ARCH_LBR) ==
kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR))
perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
?
+ x86_perf_get_lbr(&lbr);
+ if (lbr.nr)
+ perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
+ }
if (vmx_pebs_supported()) {
perf_cap |= host_perf_cap & PERF_CAP_PEBS_MASK;
base-commit: 2de154f541fc5b9f2aed3fe06e218130718ce320
