Re: [Xen-devel] [PATCH V4 2/4] x86/xsaves: enable xsaves/xrstors in xen

[Shuai Ruan <shuai.ruan@xxxxxxxxxxxxxxx>]

On Wed, Aug 26, 2015 at 07:06:00AM -0600, Jan Beulich wrote:
> >>> On 25.08.15 at 12:54, <shuai.ruan@xxxxxxxxxxxxxxx> wrote:
> 
> > +++ b/xen/arch/x86/xstate.c
> > @@ -214,6 +214,11 @@ void xsave(struct vcpu *v, uint64_t mask)
> >          typeof(ptr->fpu_sse.fip.sel) fcs = ptr->fpu_sse.fip.sel;
> >          typeof(ptr->fpu_sse.fdp.sel) fds = ptr->fpu_sse.fdp.sel;
> >  
> > +        if ( cpu_has_xsaves )
> > +            asm volatile ( ".byte 0x48,0x0f,0xc7,0x2f"
> > +                           : "=m" (*ptr)
> > +                           : "a" (lmask), "d" (hmask), "D" (ptr) );
> > +        else
> >          if ( cpu_has_xsaveopt )
> 
> Same question as above - why not also use XSAVEC when
> available?
> 
In practice no real processor exists that only has one of the
xsavec/xsaves.
> Jan
> 
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> 

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