Re: [PATCH 15/19] kvm: x86: Save and restore guest XFD_ERR properly

[Thomas Gleixner]

On Sat, Dec 11 2021 at 02:31, Paolo Bonzini wrote:
> On 12/11/21 01:10, Thomas Gleixner wrote:
>>      2) When the guest triggers #NM is takes an VMEXIT and the host
>>         does:
>> 
>>                  rdmsrl(MSR_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
>> 
>>         injects the #NM and goes on.
>> 
>>      3) When the guest writes to MSR_XFD_ERR it takes an VMEXIT and
>>         the host does:
>> 
>>             vcpu->arch.guest_fpu.xfd_err = msrval;
>>             wrmsrl(MSR_XFD_ERR, msrval);
>
> No wrmsrl here I think, the host value is 0 and should stay so.  Instead 
> the wrmsrl will happen the next time the VCPU loop is entred.

I assumed this can be handled in the fast path, but either way.