Re: [PATCH v5 04/19] KVM:x86: Refresh CPUID on write to guest MSR_IA32_XSS

Paolo Bonzini
2023-08-07T06:56:05Z

On 8/4/23 20:27, Sean Christopherson wrote:
> I think my preference is to enforce guest CPUID for host accesses to
> XSS, XFD, XFD_ERR, etc I'm pretty sure I've advocated for the exact
> opposite in the past, i.e. argued that KVM's ABI is to not enforce
> ordering between KVM_SET_CPUID2 and KVM_SET_MSR. But this is becoming
> untenable, juggling the dependencies in KVM is complex and is going
> to result in a nasty bug at some point.

Fortunately, you are right now. Well, almost :) but the important part
is that indeed the dependencies are too complex.

While host-side accesses must be allowed, they should only allow the
default value if the CPUID bit is not set.

Paolo