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@xxxxxxx>
---
arch/x86/kvm/x86.c | 24 ++++++++++++++++++++----
1 files changed, 20 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5a66bb9..7d0a0bb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -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) },
@@ -885,8 +888,15 @@ 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;
}
@@ -1032,8 +1042,14 @@ 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;
--
1.6.1.3
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