Re: [Xen-devel] [PATCH 2/2] x86/HVM: don't calculate XSTATE area sizes in software

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Jun 01, 2016 at 04:35:44PM +0100, Andrew Cooper wrote:
> On 01/06/16 16:06, Jan Beulich wrote:
> > @@ -3440,42 +3440,24 @@ void hvm_cpuid(unsigned int input, unsig
> >              *eax = *ebx = *ecx = *edx = 0;
> >              break;
> >          }
> > -        /* EBX value of main leaf 0 depends on enabled xsave features */
> > -        if ( count == 0 && v->arch.xcr0 ) 
> > -        {
> > -            /* reset EBX to default value first */
> > -            *ebx = XSTATE_AREA_MIN_SIZE; 
> > -            for ( sub_leaf = 2; sub_leaf < 63; sub_leaf++ )
> > -            {
> > -                if ( !(v->arch.xcr0 & (1ULL << sub_leaf)) )
> > -                    continue;
> > -                domain_cpuid(d, input, sub_leaf, &_eax, &_ebx, &_ecx, 
> > -                             &_edx);
> > -                if ( (_eax + _ebx) > *ebx )
> > -                    *ebx = _eax + _ebx;
> > -            }
> > -        }
> > -
> > -        if ( count == 1 )
> > +        switch ( count )
> >          {
> > +        case 1:
> >              *eax &= hvm_featureset[FEATURESET_Da1];
> > -
> > -            if ( *eax & cpufeat_mask(X86_FEATURE_XSAVES) )
> > +            if ( !(*eax & cpufeat_mask(X86_FEATURE_XSAVES)) )
> >              {
> > -                uint64_t xfeatures = v->arch.xcr0 | 
> > v->arch.hvm_vcpu.msr_xss;
> > -
> > -                *ebx = XSTATE_AREA_MIN_SIZE;
> > -                if ( xfeatures & ~XSTATE_FP_SSE )
> > -                    for ( sub_leaf = 2; sub_leaf < 63; sub_leaf++ )
> > -                        if ( xfeatures & (1ULL << sub_leaf) )
> > -                        {
> > -                            if ( test_bit(sub_leaf, &xstate_align) )
> > -                                *ebx = ROUNDUP(*ebx, 64);
> > -                            *ebx += xstate_sizes[sub_leaf];
> > -                        }
> > -            }
> > -            else
> >                  *ebx = *ecx = *edx = 0;
> > +                break;
> > +            }
> > +            /* fall through */
> > +        case 0:
> > +            /*
> > +             * Always read CPUID.0xD[ECX=0/1].EBX from hardware, rather 
> > than
> > +             * domain policy.  It varies with enabled xstate, and the 
> > correct
> > +             * xcr0/xss are in context.
> > +             */
> > +            cpuid_count(input, count, &dummy, ebx, &dummy, &dummy);
> > +            break;
> 
> It would be helpful for my PKU bugfix if you could avoid collapsing this
> into a fallthough, as the fallthough would need to be undone. 
> Otherwise, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> 

Release-acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

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