Re: [PATCH v4 18/21] kvm: x86: Add support for getting/setting expanded xstate buffer

[Paolo Bonzini]

On 1/4/22 20:46, Sean Christopherson wrote:
> On Wed, Dec 29, 2021, Yang Zhong wrote:
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index bdf89c28d2ce..76e1941db223 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -4296,6 +4296,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> >   		else
> >   			r = 0;
> >   		break;
> > +	case KVM_CAP_XSAVE2:
> > +		r = kvm->vcpus[0]->arch.guest_fpu.uabi_size;
>
> a) This does not compile against kvm/queue.
>
>     arch/x86/kvm/x86.c: In function ‘kvm_vm_ioctl_check_extension’:
>     arch/x86/kvm/x86.c:4317:24: error: ‘struct kvm’ has no member named ‘vcpus’
>      4317 |                 r = kvm->vcpus[0]->arch.guest_fpu.uabi_size;
>
> b) vcpu0 is not guaranteed to be non-NULL at this point.

Yang, you can post an incremental patch for this.  You can use the 
highest bit of the guest-permitted xcr0 (i.e. the OR of KVM's supported 
XCR0 an the guest-permitted dynamic features) and pass it to cpuid(0xD).

Paolo