Re: [PATCH 4/4] KVM: x86/cpuid: Add AMD CPUID ExtPerfMonAndDbg leaf 0x80000022
From: Like Xu
Date: Wed Sep 07 2022 - 00:00:57 EST
On 7/9/2022 4:08 am, Jim Mattson wrote:
On Tue, Sep 6, 2022 at 5:53 AM Like Xu <like.xu.linux@xxxxxxxxx> wrote:
On 6/9/2022 1:36 am, Jim Mattson wrote:
On Mon, Sep 5, 2022 at 5:45 AM Like Xu <like.xu.linux@xxxxxxxxx> wrote:
From: Sandipan Das <sandipan.das@xxxxxxx>
CPUID leaf 0x80000022 i.e. ExtPerfMonAndDbg advertises some
new performance monitoring features for AMD processors.
Bit 0 of EAX indicates support for Performance Monitoring
Version 2 (PerfMonV2) features. If found to be set during
PMU initialization, the EBX bits of the same CPUID function
can be used to determine the number of available PMCs for
different PMU types.
Expose the relevant bits via KVM_GET_SUPPORTED_CPUID so
that guests can make use of the PerfMonV2 features.
Co-developed-by: Like Xu <likexu@xxxxxxxxxxx>
Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
Signed-off-by: Sandipan Das <sandipan.das@xxxxxxx>
---
arch/x86/include/asm/perf_event.h | 8 ++++++++
arch/x86/kvm/cpuid.c | 21 ++++++++++++++++++++-
2 files changed, 28 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index f6fc8dd51ef4..c848f504e467 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -214,6 +214,14 @@ union cpuid_0x80000022_ebx {
unsigned int full;
};
+union cpuid_0x80000022_eax {
+ struct {
+ /* Performance Monitoring Version 2 Supported */
+ unsigned int perfmon_v2:1;
+ } split;
+ unsigned int full;
+};
+
struct x86_pmu_capability {
int version;
int num_counters_gp;
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 75dcf7a72605..08a29ab096d2 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1094,7 +1094,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
entry->edx = 0;
break;
case 0x80000000:
- entry->eax = min(entry->eax, 0x80000021);
+ entry->eax = min(entry->eax, 0x80000022);
/*
* Serializing LFENCE is reported in a multitude of ways, and
* NullSegClearsBase is not reported in CPUID on Zen2; help
@@ -1203,6 +1203,25 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
if (!static_cpu_has_bug(X86_BUG_NULL_SEG))
entry->eax |= BIT(6);
break;
+ /* AMD Extended Performance Monitoring and Debug */
+ case 0x80000022: {
+ union cpuid_0x80000022_eax eax;
+ union cpuid_0x80000022_ebx ebx;
+
+ entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+ if (!enable_pmu)
+ break;
+
+ if (kvm_pmu_cap.version > 1) {
+ /* AMD PerfMon is only supported up to V2 in the KVM. */
+ eax.split.perfmon_v2 = 1;
+ ebx.split.num_core_pmc = min(kvm_pmu_cap.num_counters_gp,
+ KVM_AMD_PMC_MAX_GENERIC);
Note that the number of core PMCs has to be at least 6 if
guest_cpuid_has(vcpu, X86_FEATURE_PERFCTR_CORE). I suppose this leaf
could claim fewer, but the first 6 PMCs must work, per the v1 PMU
spec. That is, software that knows about PERFCTR_CORE, but not about
PMU v2, can rightfully expect 6 PMCs.
I thought the NumCorePmc number would only make sense if
CPUID.80000022.eax.perfmon_v2
bit was present, but considering that the user space is perfectly fine with just
configuring the
NumCorePmc number without setting perfmon_v2 bit at all, so how about:
CPUID.80000022H might only make sense if X86_FEATURE_PERFCTR_CORE is
present. It's hard to know in the absence of documentation.
Whenever this happens, we may always leave the definition of behavior to the
hypervisor.
/* AMD Extended Performance Monitoring and Debug */
case 0x80000022: {
union cpuid_0x80000022_eax eax;
union cpuid_0x80000022_ebx ebx;
bool perfctr_core;
entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
if (!enable_pmu)
break;
perfctr_core = kvm_cpu_cap_has(X86_FEATURE_PERFCTR_CORE);
if (!perfctr_core)
ebx.split.num_core_pmc = AMD64_NUM_COUNTERS;
if (kvm_pmu_cap.version > 1) {
/* AMD PerfMon is only supported up to V2 in the KVM. */
eax.split.perfmon_v2 = 1;
ebx.split.num_core_pmc = min(kvm_pmu_cap.num_counters_gp,
KVM_AMD_PMC_MAX_GENERIC);
}
if (perfctr_core) {
ebx.split.num_core_pmc = max(ebx.split.num_core_pmc,
AMD64_NUM_COUNTERS_CORE);
}
This still isn't quite right. All AMD CPUs must support a minimum of 4 PMCs.
K7 at least. I could not confirm that all antique AMD CPUs have 4 counters w/o
perfctr_core.
entry->eax = eax.full;
entry->ebx = ebx.full;
break;
}
?
Once 0x80000022 appears, ebx.split.num_core_pmc will report only
the real "Number of Core Performance Counters" regardless of perfmon_v2.
+ }
+ entry->eax = eax.full;
+ entry->ebx = ebx.full;
+ break;
+ }
/*Add support for Centaur's CPUID instruction*/
case 0xC0000000:
/*Just support up to 0xC0000004 now*/
--
2.37.3