KVM: introduce module parameter for ignoring unknown MSRs accesses (ed85c068) · Commits · 戴 / test

KVM will inject a #GP into the guest if that tries to access unhandled MSRs. This will crash many guests. Although it would be the correct way to actually handle these MSRs, we introduce a runtime switchable module param called "ignore_msrs" (defaults to 0). If this is Y, unknown MSR reads will return 0, while MSR writes are simply dropped. In both cases we print a message to dmesg to inform the user about that. You can change the behaviour at any time by saying: # echo 1 > /sys/modules/kvm/parameters/ignore_msrs Signed-off-by:

Andre Przywara <andre.przywara@amd.com> Signed-off-by:

Avi Kivity <avi@redhat.com>

arch/x86/kvm/x86.c

+20 −4

Original line number	Diff line number	Diff line
		@@ -83,6 +83,9 @@ struct kvm_cpuid_entry2 kvm_find_cpuid_entry(struct kvm_vcpu vcpu,
		struct kvm_x86_ops *kvm_x86_ops;
		EXPORT_SYMBOL_GPL(kvm_x86_ops);

		int ignore_msrs = 0;
		module_param_named(ignore_msrs, ignore_msrs, bool, S_IRUGO \| S_IWUSR);

		struct kvm_stats_debugfs_item debugfs_entries[] = {
		{ "pf_fixed", VCPU_STAT(pf_fixed) },
		{ "pf_guest", VCPU_STAT(pf_guest) },
		@@ -930,8 +933,15 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
		"0x%x data 0x%llx\n", msr, data);
		break;
		default:
		pr_unimpl(vcpu, "unhandled wrmsr: 0x%x data %llx\n", msr, data);
		if (!ignore_msrs) {
		pr_unimpl(vcpu, "unhandled wrmsr: 0x%x data %llx\n",
		msr, data);
		return 1;
		} else {
		pr_unimpl(vcpu, "ignored wrmsr: 0x%x data %llx\n",
		msr, data);
		break;
		}
		}
		return 0;
		}
		@@ -1078,8 +1088,14 @@ int kvm_get_msr_common(struct kvm_vcpu vcpu, u32 msr, u64 pdata)
		case MSR_IA32_MC0_CTL ... MSR_IA32_MC0_CTL + 4 * KVM_MAX_MCE_BANKS - 1:
		return get_msr_mce(vcpu, msr, pdata);
		default:
		if (!ignore_msrs) {
		pr_unimpl(vcpu, "unhandled rdmsr: 0x%x\n", msr);
		return 1;
		} else {
		pr_unimpl(vcpu, "ignored rdmsr: 0x%x\n", msr);
		data = 0;
		}
		break;
		}
		*pdata = data;
		return 0;

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