KVM: x86: omit absent pmu MSRs from MSR list

INTEL_PMC_MAX_GENERIC is currently 32, which exceeds the 18 contiguous
MSR indices reserved by Intel for event selectors.  Since some machines
actually have MSRs past the reserved range, these may survive the
filtering of msrs_to_save array and would be rejected by KVM_GET/SET_MSR.
To avoid this, cut the list to whatever CPUID reports for the host's
architectural PMU.
Reported-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Suggested-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Jim Mattson <jmattson@google.com>
Fixes: e2ada66e ("kvm: x86: Add Intel PMU MSRs to msrs_to_save[]", 2019-08-21)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -5105,13 +5105,14 @@ long kvm_arch_vm_ioctl(struct file *filp,
 
 static void kvm_init_msr_list(void)
 {
+	struct x86_pmu_capability x86_pmu;
 	u32 dummy[2];
 	unsigned i, j;
 
 	BUILD_BUG_ON_MSG(INTEL_PMC_MAX_FIXED != 4,
 			 "Please update the fixed PMCs in msrs_to_save[]");
-	BUILD_BUG_ON_MSG(INTEL_PMC_MAX_GENERIC != 32,
-			 "Please update the generic perfctr/eventsel MSRs in msrs_to_save[]");
+
+	perf_get_x86_pmu_capability(&x86_pmu);
 
 	for (i = j = 0; i < ARRAY_SIZE(msrs_to_save); i++) {
 		if (rdmsr_safe(msrs_to_save[i], &dummy[0], &dummy[1]) < 0)
@@ -5153,6 +5154,15 @@ static void kvm_init_msr_list(void)
 				intel_pt_validate_hw_cap(PT_CAP_num_address_ranges) * 2)
 				continue;
 			break;
+		case MSR_ARCH_PERFMON_PERFCTR0 ... MSR_ARCH_PERFMON_PERFCTR0 + 31:
+			if (msrs_to_save[i] - MSR_ARCH_PERFMON_PERFCTR0 >=
+			    min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
+				continue;
+			break;
+		case MSR_ARCH_PERFMON_EVENTSEL0 ... MSR_ARCH_PERFMON_EVENTSEL0 + 31:
+			if (msrs_to_save[i] - MSR_ARCH_PERFMON_EVENTSEL0 >=
+			    min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
+				continue;
 		}
 		default:
 			break;