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 09:50:10AM -0600, Jan Beulich wrote:
> >>> On 01.06.16 at 17:35, <andrew.cooper3@xxxxxxxxxx> 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>
> 
> Converting this back is easy to do, but I'll nevertheless wait for
> Wei's opinion re 4.7 inclusion, as otherwise I'll eventually need to
> rebase on top of yours anyway.
> 

I think this is fine for 4.7. And I will leave it to you two to
coordinate the rest.

Wei.

> Jan
> 

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