KVM: x86/svm: Add module param to control PMU virtualization

For Intel, the guest PMU can be disabled via clearing the PMU CPUID.
For AMD, all hw implementations support the base set of four
performance counters, with current mainstream hardware indicating
the presence of two additional counters via X86_FEATURE_PERFCTR_CORE.

In the virtualized world, the AMD guest driver may detect
the presence of at least one counter MSR. Most hypervisor
vendors would introduce a module param (like lbrv for svm)
to disable PMU for all guests.

Another control proposal per-VM is to pass PMU disable information
via MSR_IA32_PERF_CAPABILITIES or one bit in CPUID Fn4000_00[FF:00].
Both of methods require some guest-side changes, so a module
parameter may not be sufficiently granular, but practical enough.
Signed-off-by: Like Xu <likexu@tencent.com>
Message-Id: <20211117080304.38989-1-likexu@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/cpuid.c

@@ -523,7 +523,7 @@ void kvm_set_cpu_caps(void)
 		F(CR8_LEGACY) | F(ABM) | F(SSE4A) | F(MISALIGNSSE) |
 		F(3DNOWPREFETCH) | F(OSVW) | 0 /* IBS */ | F(XOP) |
 		0 /* SKINIT, WDT, LWP */ | F(FMA4) | F(TBM) |
-		F(TOPOEXT) | F(PERFCTR_CORE)
+		F(TOPOEXT) | 0 /* PERFCTR_CORE */
 	);
 
 	kvm_cpu_cap_mask(CPUID_8000_0001_EDX,

arch/x86/kvm/svm/pmu.c

@@ -16,6 +16,7 @@
 #include "cpuid.h"
 #include "lapic.h"
 #include "pmu.h"
+#include "svm.h"
 
 enum pmu_type {
 	PMU_TYPE_COUNTER = 0,
@@ -100,6 +101,9 @@ static inline struct kvm_pmc *get_gp_pmc_amd(struct kvm_pmu *pmu, u32 msr,
 {
 	struct kvm_vcpu *vcpu = pmu_to_vcpu(pmu);
 
+	if (!pmu)
+		return NULL;
+
 	switch (msr) {
 	case MSR_F15H_PERF_CTL0:
 	case MSR_F15H_PERF_CTL1:

arch/x86/kvm/svm/svm.c

@@ -192,6 +192,10 @@ module_param(vgif, int, 0444);
 static int lbrv = true;
 module_param(lbrv, int, 0444);
 
+/* enable/disable PMU virtualization */
+bool pmu = true;
+module_param(pmu, bool, 0444);
+
 static int tsc_scaling = true;
 module_param(tsc_scaling, int, 0444);
 
@@ -954,6 +958,10 @@ static __init void svm_set_cpu_caps(void)
 	    boot_cpu_has(X86_FEATURE_AMD_SSBD))
 		kvm_cpu_cap_set(X86_FEATURE_VIRT_SSBD);
 
+	/* AMD PMU PERFCTR_CORE CPUID */
+	if (pmu && boot_cpu_has(X86_FEATURE_PERFCTR_CORE))
+		kvm_cpu_cap_set(X86_FEATURE_PERFCTR_CORE);
+
 	/* CPUID 0x8000001F (SME/SEV features) */
 	sev_set_cpu_caps();
 }
@@ -1087,6 +1095,9 @@ static __init int svm_hardware_setup(void)
 			pr_info("LBR virtualization supported\n");
 	}
 
+	if (!pmu)
+		pr_info("PMU virtualization is disabled\n");
+
 	svm_set_cpu_caps();
 
 	/*

arch/x86/kvm/svm/svm.h

@@ -32,6 +32,7 @@
 extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
 extern bool npt_enabled;
 extern bool intercept_smi;
+extern bool pmu;
 
 /*
  * Clean bits in VMCB.