[PATCH] KVM: x86: svm: report MSR_IA32_MCG_EXT_CTL as unsupported

[PATCH] KVM: x86: svm: report MSR_IA32_MCG_EXT_CTL as unsupported

[Vitaly Kuznetsov]

AMD doesn't seem to implement MSR_IA32_MCG_EXT_CTL and svm code in kvm
knows nothing about it, however, this MSR is among emulated_msrs and
thus returned with KVM_GET_MSR_INDEX_LIST. The consequent KVM_GET_MSRS,
of course, fails.

Report the MSR as unsupported to not confuse userspace.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/kvm/svm.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 2acb42b74a51..dfdf7d0b7f88 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5845,6 +5845,13 @@ static bool svm_cpu_has_accelerated_tpr(void)
 
 static bool svm_has_emulated_msr(int index)
 {
+	switch (index) {
+	case MSR_IA32_MCG_EXT_CTL:
+		return false;
+	default:
+		break;
+	}
+
 	return true;
 }
 
-- 
2.19.2

Re: [PATCH] KVM: x86: svm: report MSR_IA32_MCG_EXT_CTL as unsupported

[Radim Krčmář]

2018-12-19 12:06+0100, Vitaly Kuznetsov:
> AMD doesn't seem to implement MSR_IA32_MCG_EXT_CTL and svm code in kvm
> knows nothing about it, however, this MSR is among emulated_msrs and
> thus returned with KVM_GET_MSR_INDEX_LIST. The consequent KVM_GET_MSRS,
> of course, fails.
> 
> Report the MSR as unsupported to not confuse userspace.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  arch/x86/kvm/svm.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 2acb42b74a51..dfdf7d0b7f88 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5845,6 +5845,13 @@ static bool svm_cpu_has_accelerated_tpr(void)
>  
>  static bool svm_has_emulated_msr(int index)
>  {
> +	switch (index) {
> +	case MSR_IA32_MCG_EXT_CTL:
> +		return false;
> +	default:
> +		break;

Queued, thanks.

Btw, I would prefer this without the

  default: break;

as I don't think we'll ever add something there.

Re: [PATCH] KVM: x86: svm: report MSR_IA32_MCG_EXT_CTL as unsupported

[Vitaly Kuznetsov]

Radim Krčmář <rkrcmar@redhat.com> writes:

> 2018-12-19 12:06+0100, Vitaly Kuznetsov:
>> AMD doesn't seem to implement MSR_IA32_MCG_EXT_CTL and svm code in kvm
>> knows nothing about it, however, this MSR is among emulated_msrs and
>> thus returned with KVM_GET_MSR_INDEX_LIST. The consequent KVM_GET_MSRS,
>> of course, fails.
>> 
>> Report the MSR as unsupported to not confuse userspace.
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>>  arch/x86/kvm/svm.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>> 
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 2acb42b74a51..dfdf7d0b7f88 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -5845,6 +5845,13 @@ static bool svm_cpu_has_accelerated_tpr(void)
>>  
>>  static bool svm_has_emulated_msr(int index)
>>  {
>> +	switch (index) {
>> +	case MSR_IA32_MCG_EXT_CTL:
>> +		return false;
>> +	default:
>> +		break;
>
> Queued, thanks.
>
> Btw, I would prefer this without the
>
>   default: break;
>
> as I don't think we'll ever add something there.

"640K ought to be enough for anybody" :-)

But in case you commit it as

return index != MSR_IA32_MCG_EXT_CTL; 

I won't object. Thanks,

-- 
Vitaly

Re: [PATCH] KVM: x86: svm: report MSR_IA32_MCG_EXT_CTL as unsupported

[Paolo Bonzini]

On 21/12/18 11:06, Vitaly Kuznetsov wrote:
>> Btw, I would prefer this without the
>>
>>   default: break;
>>
>> as I don't think we'll ever add something there.
> 
> "640K ought to be enough for anybody" :-)
> 
> But in case you commit it as
> 
> return index != MSR_IA32_MCG_EXT_CTL; 
> 
> I won't object. Thanks,

Radim committed it as it, but I think he did want the switch statement
(hey, vmx_has_emulated_msr has *two* cases!).  It's just the "default:
break;" that is unnecessary or could be "default: return true;".

Paolo