Re: [PATCH] KVM: x86: Fix the #GP(0) and #UD conditions for XSETBV emulation

[Paolo Bonzini]

On 1/17/22 10:44, Like Xu wrote:
> > Also, the "Fixes" tag is not really correct as the behavior was the 
> > same before.  Rather, it fixes commit 02d4160fbd76 ("x86: KVM: add 
> > xsetbv to the 
>
> It seems the original code comes from 81dd35d42c9a ("KVM: SVM: Add 
> xsetbv intercept").
> 2acf923e38 ("KVM: VMX: Enable XSAVE/XRSTOR for guest") and 92f9895c146d.
>
> > emulator", 2019-08-22).  Checking OSXSAVE is a bug in the emulator 
> > path, even though it's not needed in the XSETBV vmexit case.
>
> The kvm_emulate_xsetbv() has been removed from the emulator path.
> I'm not really sure why it's not needed in the XSETBV vmexit case. More 
> details ?

Nevermind, I confused AMD (where #UD is generated before checking for 
exceptions) with Intel where it's unconditional.

So the bug should be there since 2acf923e38 by executing XSETBV with 
CR4.XSAVE=0.  If so, please include a testcase.

Paolo

> > Thanks,
> >
> > Paolo
> >
> > > +    if ((is_protmode(vcpu) && static_call(kvm_x86_get_cpl)(vcpu) != 
> > > 0) ||
> > >           __kvm_set_xcr(vcpu, kvm_rcx_read(vcpu), 
> > > kvm_read_edx_eax(vcpu))) {
> > >           kvm_inject_gp(vcpu, 0);
> > >           return 1;