Re: [PATCH 1/7] target/i386: disable PerfMonV2 when PERFCORE unavailable

[Zhao Liu <zhao1.liu@intel.com>]

Hi Dongli,

On Mon, Nov 04, 2024 at 01:40:16AM -0800, Dongli Zhang wrote:
> Date: Mon,  4 Nov 2024 01:40:16 -0800
> From: Dongli Zhang <dongli.zhang@oracle.com>
> Subject: [PATCH 1/7] target/i386: disable PerfMonV2 when PERFCORE
>  unavailable
> X-Mailer: git-send-email 2.43.5
> 
> When the PERFCORE is disabled with "-cpu host,-perfctr-core", it is
> reflected in in guest dmesg.
> 
> [    0.285136] Performance Events: AMD PMU driver.
> 
> However, the guest cpuid indicates the PerfMonV2 is still available.
> 
> CPU:
>    Extended Performance Monitoring and Debugging (0x80000022):
>       AMD performance monitoring V2         = true
>       AMD LBR V2                            = false
>       AMD LBR stack & PMC freezing          = false
>       number of core perf ctrs              = 0x6 (6)
>       number of LBR stack entries           = 0x0 (0)
>       number of avail Northbridge perf ctrs = 0x0 (0)
>       number of available UMC PMCs          = 0x0 (0)
>       active UMCs bitmask                   = 0x0
> 
> Disable PerfMonV2 in cpuid when PERFCORE is disabled.
> 
> Fixes: 209b0ac12074 ("target/i386: Add PerfMonV2 feature bit")
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
>  target/i386/cpu.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 3baa95481f..4490a7a8d6 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -7103,6 +7103,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
>          *eax = *ebx = *ecx = *edx = 0;
>          /* AMD Extended Performance Monitoring and Debug */
>          if (kvm_enabled() && cpu->enable_pmu &&
> +            (env->features[FEAT_8000_0001_ECX] & CPUID_EXT3_PERFCORE) &&
>              (env->features[FEAT_8000_0022_EAX] & CPUID_8000_0022_EAX_PERFMON_V2)) {
>              *eax |= CPUID_8000_0022_EAX_PERFMON_V2;
>              *ebx |= kvm_arch_get_supported_cpuid(cs->kvm_state, index, count,

You can define dependency like this:

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 3baa95481fbc..99c69ec9f369 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -1803,6 +1803,10 @@ static FeatureDep feature_dependencies[] = {
         .from = { FEAT_7_1_EDX,             CPUID_7_1_EDX_AVX10 },
         .to = { FEAT_24_0_EBX,              ~0ull },
     },
+    {
+        .from = { FEAT_8000_0001_ECX,       CPUID_EXT3_PERFCORE },
+        .to = { FEAT_8000_0022_EAX,         CPUID_8000_0022_EAX_PERFMON_V2 }
+    }
 };

 typedef struct X86RegisterInfo32 {

---
Does this meet your needs?

Regards,
Zhao