[PATCH v7 1/9] target/i386: disable PerfMonV2 when PERFCORE unavailable

Dongli Zhang
2025-11-11T06:20:21Z

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.

Suggested-by: Zhao Liu <zhao1.liu@intel.com>
Fixes: 209b0ac12074 ("target/i386: Add PerfMonV2 feature bit")
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Sandipan Das <sandipan.das@amd.com>
---
Changed since v1:
- Use feature_dependencies (suggested by Zhao Liu).
Changed since v2:
- Nothing. Zhao and Xiaoyao may move it to x86_cpu_expand_features()
later.

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

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 6417775786..3653f8953e 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -1994,6 +1994,10 @@ 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 {
--
2.39.3