On 03/11/2015 05:47 PM, Luck, Tony wrote:
>> When running as a guest under kvm, it's possible that the MSR
>> being accessed may not be implemented. All MSR accesses should
>> be prepared to handle exceptions.
> Isn't that a KVM bug? The code here first checks family/model before
> accessing the MSR:
>
> if (c->x86 == 0x15 &&
> (c->x86_model >= 0x10 && c->x86_model <= 0x1f)) {
>
> If kvm tells the guest that it is running on one of these models, shouldn't
> it provide
> complete coverage for that model?
These MSRs don't make sense in guest mode. The real question is if we
fix that in KVM, here, or both. I'm a fan of fixing it in both places.
Xen's behavior is to return a value of 0 if the guest tries to access
these, that seems like a reasonable thing to do in KVM as well. I am
volunteering myself to write that patch for KVM, but I would encourage
accepting an updated version of this patch as well.
>
> If that isn't possible - then you should still do more than just
> s/rdmsrl/rdmsrl_safe/ ... like
> check the return value to see whether you got an exception .. and thus should
> skip past
> code that uses the "val" that you thought you read from the non-existent MSR.
Initializing val to 0 where it is declared should have the desired effect.
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