[v4] target/i386/kvm/pmu: PMU Enhancement, Bugfix and Cleanup

[PATCH v4 03/11] target/i386: disable PERFCORE when "-pmu" is configured

Posted by Dongli Zhang 8 months ago

Currently, AMD PMU support isn't determined based on CPUID, that is, the
"-pmu" option does not fully disable KVM AMD PMU virtualization.

To minimize AMD PMU features, remove PERFCORE when "-pmu" is configured.

To completely disable AMD PMU virtualization will be implemented via
KVM_CAP_PMU_CAPABILITY in upcoming patches.

As a reminder, neither CPUID_EXT3_PERFCORE nor
CPUID_8000_0022_EAX_PERFMON_V2 is removed from env->features[] when "-pmu"
is configured. Developers should query whether they are supported via
cpu_x86_cpuid() rather than relying on env->features[] in future patches.

Suggested-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
---
Changed since v2:
  - No need to check "kvm_enabled() && IS_AMD_CPU(env)".

 target/i386/cpu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 2b87331be5..acbd627f7e 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -7242,6 +7242,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
             !(env->hflags & HF_LMA_MASK)) {
             *edx &= ~CPUID_EXT2_SYSCALL;
         }
+
+        if (!cpu->enable_pmu) {
+            *ecx &= ~CPUID_EXT3_PERFCORE;
+        }
         break;
     case 0x80000002:
     case 0x80000003:
-- 
2.39.3

Re: [PATCH v4 03/11] target/i386: disable PERFCORE when "-pmu" is configured

Posted by Sandipan Das 7 months, 4 weeks ago

On 4/17/2025 3:22 AM, Dongli Zhang wrote:
> Currently, AMD PMU support isn't determined based on CPUID, that is, the
> "-pmu" option does not fully disable KVM AMD PMU virtualization.
> 
> To minimize AMD PMU features, remove PERFCORE when "-pmu" is configured.
> 
> To completely disable AMD PMU virtualization will be implemented via
> KVM_CAP_PMU_CAPABILITY in upcoming patches.
> 
> As a reminder, neither CPUID_EXT3_PERFCORE nor
> CPUID_8000_0022_EAX_PERFMON_V2 is removed from env->features[] when "-pmu"
> is configured. Developers should query whether they are supported via
> cpu_x86_cpuid() rather than relying on env->features[] in future patches.
> 
> Suggested-by: Zhao Liu <zhao1.liu@intel.com>
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
> ---
> Changed since v2:
>   - No need to check "kvm_enabled() && IS_AMD_CPU(env)".
> 
>  target/i386/cpu.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 

Reviewed-by: Sandipan Das <sandipan.das@amd.com>