Re: [PATCH v6 1/2] xen/hvm: introduce a flags field in the CPU save record

["Roger Pau Monné" <roger.pau@citrix.com>]

El 12/01/16 a les 17.31, Jan Beulich ha escrit:
>>>> On 12.01.16 at 17:12, <roger.pau@citrix.com> wrote:
>> @@ -2087,19 +2100,21 @@ static int hvm_load_cpu_ctxt(struct domain *d, hvm_domain_context_t *h)
>>      seg.attr.bytes = ctxt.ldtr_arbytes;
>>      hvm_set_segment_register(v, x86_seg_ldtr, &seg);
>>  
>> -    /* In case xsave-absent save file is restored on a xsave-capable host */
>> -    if ( cpu_has_xsave && !xsave_enabled(v) )
>> +    v->fpu_initialised = !!(ctxt.flags & XEN_X86_FPU_INITIALISED);
>> +    if ( v->fpu_initialised )
>>      {
>> -        struct xsave_struct *xsave_area = v->arch.xsave_area;
>> +        memcpy(v->arch.fpu_ctxt, ctxt.fpu_regs, sizeof(ctxt.fpu_regs));
>> +        /* In case xsave-absent save file is restored on a xsave-capable host */
>> +        if ( cpu_has_xsave && !xsave_enabled(v) )
>> +        {
>> +            struct xsave_struct *xsave_area = v->arch.xsave_area;
>>  
>> -        memcpy(v->arch.xsave_area, ctxt.fpu_regs, sizeof(ctxt.fpu_regs));
>> -        xsave_area->xsave_hdr.xstate_bv = XSTATE_FP_SSE;
>> -        if ( cpu_has_xsaves || cpu_has_xsavec )
>> -            xsave_area->xsave_hdr.xcomp_bv = XSTATE_FP_SSE |
>> -                                             XSTATE_COMPACTION_ENABLED;
>> +            xsave_area->xsave_hdr.xstate_bv = XSTATE_FP_SSE;
>> +            if ( cpu_has_xsaves || cpu_has_xsavec )
>> +                xsave_area->xsave_hdr.xcomp_bv = XSTATE_FP_SSE |
>> +                                                 XSTATE_COMPACTION_ENABLED;
>> +        }
>>      }
>> -    else
>> -        memcpy(v->arch.fpu_ctxt, ctxt.fpu_regs, sizeof(ctxt.fpu_regs));
>>  
> 
> I would have expected this to simply be re-indentation, yet
> you changed from if/else to just if with the else code done
> ahead of it. If this really is intended, the commit message should
> explain it.

Right, sorry. AFAICT v->arch.fpu_ctxt points to the xsave_area (as set
by vcpu_init_fpu), so I though it was simpler to just do one memcpy for
both cases, since v->arch.fpu_ctxt always points to the right area for
either cases (and I was already modifying the code in question).

I can see that this might be seen as an unrelated change, so if you want
I can split it into a separate patch, or add the following to the commit
message:

"While modifying the FPU restore part of hvm_load_cpu_ctxt remove the
memcpy branching, since v->arch.fpu_ctxt will always point to the right
area for hosts with XSAVE or without it."

Thanks, Roger.