Re: [Xen-devel] [PATCH v3 2/4] x86emul: Support vpclmulqdq

[Yang Zhong <yang.zhong@xxxxxxxxx>]

On Mon, Nov 27, 2017 at 08:53:24AM -0700, Jan Beulich wrote:
> >>> On 10.11.17 at 11:36, <yang.zhong@xxxxxxxxx> wrote:
> > @@ -7672,7 +7673,12 @@ x86_emulate(
> >          host_and_vcpu_must_have(pclmulqdq);
> >          if ( vex.opcx == vex_none )
> >              goto simd_0f3a_common;
> > -        generate_exception_if(vex.l, EXC_UD);
> > +        if ( !vex.l )
> > +        {
> > +            generate_exception_if(vex.l, EXC_UD);
> 
> What's the point of this?

  Jan, thanks for your help!
  generate_exception_if(vex.l, EXC_UD) in here is not any useful,
  i will remove it, thanks!

> 
> > +            goto simd_0f_imm8_avx;
> > +        }
> > +        host_and_vcpu_must_have(vpclmulqdq);
> 
> Why not simply
> 
>         if ( vex.l )
>             host_and_vcpu_must_have(vpclmulqdq);
> 
  The new patch will like below:

      host_and_vcpu_must_have(pclmulqdq);
      if ( vex.opcx == vex_none )
          goto simd_0f3a_common;
+     if ( !vex.l )
+         goto simd_0f_imm8_avx;
+     host_and_vcpu_must_have(vpclmulqdq);
      goto simd_0f_imm8_ymm;

      simd_0f_imm8_ymm will be new created, which like simd_of_ymm did in the 
code.
> 
> Jan

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