Re: [PATCH 2/3 v2] XSAVE/XRSTOR: fix frozen states

[Weidong Han <weidong.han@intel.com>]

Jan Beulich wrote:
>>>> On 31.08.10 at 16:52, "Han, Weidong" <weidong.han@intel.com> wrote:
>>>>         
>> --- a/xen/include/asm-x86/i387.h	Tue Aug 31 18:12:03 2010 -0400
>> +++ b/xen/include/asm-x86/i387.h	Tue Aug 31 18:20:46 2010 -0400
>> @@ -113,9 +113,9 @@ static inline void setup_fpu(struct vcpu
>>             if ( !v->fpu_initialised )
>>                 v->fpu_initialised = 1;
>>
>> -            set_xcr0(v->arch.hvm_vcpu.xcr0 | XSTATE_FP_SSE);
>> +            /* Restore all supported feature states */
>> +            set_xcr0(xfeature_mask);
>>             xrstor(v);
>> -            set_xcr0(v->arch.hvm_vcpu.xcr0);
>>         }
>>         else
>>         {
>>     
>
> Aren't you taking away control from the guest OS of what part of the
> state it wants/needs to save?
>
>   
To fix 'frozen states', it needs to saves/restores all supported states.

I find an issue here. It should set_xcr0 to hvm_vcpu.xcr0 after xsave() 
and xrstor(), because applications in guest may read xcr0. I will fix it 
in next version.

Regards,
Weidong