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KVM: introduce module parameter for ignoring unknown MSRs accesses 

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>
This commit is contained in:
Andre Przywara 2009-06-25 12:36:49 +02:00 committed by Avi Kivity
parent 1fdbd48c24
commit ed85c06853
1 changed files with 20 additions and 4 deletions
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24
arch/x86/kvm/x86.c
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@ -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);
return 1;
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:
pr_unimpl(vcpu, "unhandled rdmsr: 0x%x\n", msr);
return 1;
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;