2018-12-19 14:44:04

by Vitaly Kuznetsov

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

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 <[email protected]>
---
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

2018-12-21 10:02:00

by Radim Krčmář

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

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 <[email protected]>
> ---
> 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.

2018-12-21 16:08:30

by Vitaly Kuznetsov

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

Radim Krčmář <[email protected]> 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 <[email protected]>
>> ---
>> 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

2018-12-21 16:32:57

by Paolo Bonzini

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

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