On 03/02/21 07:50, Like Xu wrote:
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;
This is incorrect in the case where cpu_has_vmx_lbr() is false. You
would need something like
u64 perf_cap = 0;
u64 host_perf_cap = 0;
if (boot_cpu_has(X86_FEATURE_PDCM))
rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
if (cpu_has_vmx_lbr())
perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT;
However, KVM won't run without VM_ENTRY_LOAD_DEBUG_CONTROLS and
VM_EXIT_SAVE_DEBUG_CONTROLS (see setup_vmcs_config), so this change is
not needed either.
Paolo
