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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.08.15 at 12:54, <shuai.ruan@xxxxxxxxxxxxxxx> wrote:
> 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.

No today. And in any event - there are two feature flags, so both
should be honored independently.

Jan


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