Re: [PATCH v3 2/8] KVM: x86: Clear all supported MPX xfeatures if they are not all set

[Sean Christopherson <seanjc@google.com>]

On Thu, Mar 23, 2023, Mingwei Zhang wrote:
> > --- a/arch/x86/kvm/x86.h
> > +++ b/arch/x86/kvm/x86.h
> > @@ -3,6 +3,7 @@
> >  #define ARCH_X86_KVM_X86_H
> >
> >  #include <linux/kvm_host.h>
> > +#include <asm/fpu/xstate.h>
> >  #include <asm/mce.h>
> >  #include <asm/pvclock.h>
> >  #include "kvm_cache_regs.h"
> > @@ -325,7 +326,22 @@ extern bool enable_pmu;
> >   */
> >  static inline u64 kvm_get_filtered_xcr0(void)
> >  {
> > -       return kvm_caps.supported_xcr0 & xstate_get_guest_group_perm();
> > +       u64 supported_xcr0 = kvm_caps.supported_xcr0;
> > +
> > +       BUILD_BUG_ON(XFEATURE_MASK_USER_DYNAMIC != XFEATURE_MASK_XTILE_DATA);
> > +
> > +       if (supported_xcr0 & XFEATURE_MASK_USER_DYNAMIC) {
> > +               supported_xcr0 &= xstate_get_guest_group_perm();
> > +
> > +               /*
> > +                * Treat XTILE_CFG as unsupported if the current process isn't
> > +                * allowed to use XTILE_DATA, as attempting to set XTILE_CFG in
> > +                * XCR0 without setting XTILE_DATA is architecturally illegal.
> > +                */
> > +               if (!(supported_xcr0 & XFEATURE_MASK_XTILE_DATA))
> > +                       supported_xcr0 &= XFEATURE_MASK_XTILE_CFG;
> 
> should be this? supported_xcr0 &= ~XFEATURE_MASK_XTILE_CFG;

Doh, yes.