KVM: x86/pmu: Restrict advanced features based on module enable_pmu

Once vPMU is disabled, the KVM would not expose features like:
PEBS (via clear kvm_pmu_cap.pebs_ept), legacy LBR and ARCH_LBR,
CPUID 0xA leaf, PDCM bit and MSR_IA32_PERF_CAPABILITIES, plus
PT_MODE_HOST_GUEST mode.

What this group of features has in common is that their use
relies on the underlying PMU counter and the host perf_event as a
back-end resource requester or sharing part of the irq delivery path.
Signed-off-by: Like Xu <likexu@tencent.com>
Message-Id: <20220601031925.59693-2-likexu@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/pmu.h

@@ -170,9 +170,11 @@ static inline void kvm_init_pmu_capability(void)
 	  * For Intel, only support guest architectural pmu
 	  * on a host with architectural pmu.
 	  */
-	if ((is_intel && !kvm_pmu_cap.version) || !kvm_pmu_cap.num_counters_gp) {
-		memset(&kvm_pmu_cap, 0, sizeof(kvm_pmu_cap));
+	if ((is_intel && !kvm_pmu_cap.version) || !kvm_pmu_cap.num_counters_gp)
 		enable_pmu = false;
+
+	if (!enable_pmu) {
+		memset(&kvm_pmu_cap, 0, sizeof(kvm_pmu_cap));
 		return;
 	}
 

arch/x86/kvm/vmx/capabilities.h

@@ -7,6 +7,7 @@
 #include "lapic.h"
 #include "x86.h"
 #include "pmu.h"
+#include "cpuid.h"
 
 extern bool __read_mostly enable_vpid;
 extern bool __read_mostly flexpriority_enabled;
@@ -409,6 +410,9 @@ static inline u64 vmx_get_perf_capabilities(void)
 	u64 perf_cap = PMU_CAP_FW_WRITES;
 	u64 host_perf_cap = 0;
 
+	if (!enable_pmu)
+		return 0;
+
 	if (boot_cpu_has(X86_FEATURE_PDCM))
 		rdmsrl(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
 

arch/x86/kvm/vmx/vmx.c

@@ -7568,6 +7568,9 @@ static __init void vmx_set_cpu_caps(void)
 		kvm_cpu_cap_check_and_set(X86_FEATURE_DTES64);
 	}
 
+	if (!enable_pmu)
+		kvm_cpu_cap_clear(X86_FEATURE_PDCM);
+
 	if (!enable_sgx) {
 		kvm_cpu_cap_clear(X86_FEATURE_SGX);
 		kvm_cpu_cap_clear(X86_FEATURE_SGX_LC);
@@ -8233,7 +8236,7 @@ static __init int hardware_setup(void)
 
 	if (pt_mode != PT_MODE_SYSTEM && pt_mode != PT_MODE_HOST_GUEST)
 		return -EINVAL;
-	if (!enable_ept || !cpu_has_vmx_intel_pt())
+	if (!enable_ept || !enable_pmu || !cpu_has_vmx_intel_pt())
 		pt_mode = PT_MODE_SYSTEM;
 	if (pt_mode == PT_MODE_HOST_GUEST)
 		vmx_init_ops.handle_intel_pt_intr = vmx_handle_intel_pt_intr;