[PATCH] KVM: vmx/pmu: Add VMCS fields check before exposing LBR_FMT

[Like Xu]

Before KVM exposes guest LBR_FMT perf capabilities, it needs to check
whether VMCS has GUEST_IA32_DEBUGCTL guest status field and vmx switch
support on IA32_DEBUGCTL MSR (including VM_EXIT_SAVE_DEBUG_CONTROLS
and VM_ENTRY_LOAD_DEBUG_CONTROLS). It helps nested LBR enablement.

Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
---
 arch/x86/kvm/vmx/capabilities.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index d1d77985e889..ac3af06953a8 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -378,6 +378,12 @@ static inline bool vmx_pt_mode_is_host_guest(void)
 	return pt_mode == PT_MODE_HOST_GUEST;
 }
 
+static inline bool cpu_has_vmx_lbr(void)
+{
+	return (vmcs_config.vmexit_ctrl & VM_EXIT_SAVE_DEBUG_CONTROLS) &&
+		(vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_DEBUG_CONTROLS);
+}
+
 static inline u64 vmx_get_perf_capabilities(void)
 {
 	u64 perf_cap = 0;
@@ -385,7 +391,8 @@ static inline u64 vmx_get_perf_capabilities(void)
 	if (boot_cpu_has(X86_FEATURE_PDCM))
 		rdmsrl(MSR_IA32_PERF_CAPABILITIES, perf_cap);
 
-	perf_cap &= PMU_CAP_LBR_FMT;
+	if (cpu_has_vmx_lbr())
+		perf_cap &= PMU_CAP_LBR_FMT;
 
 	/*
 	 * Since counters are virtualized, KVM would support full
-- 
2.29.2