Re: [Xen-devel] [PATCHv2 2/3] x86/fpu: Add a per-domain field to set the width of FIP/FDP

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.02.16 at 12:05, <david.vrabel@xxxxxxxxxx> wrote:
> @@ -292,17 +296,17 @@ void xsave(struct vcpu *v, uint64_t mask)
>              asm volatile ( "fnstenv %0" : "=m" (fpu_env) );
>              ptr->fpu_sse.fip.sel = fpu_env.fcs;
>              ptr->fpu_sse.fdp.sel = fpu_env.fds;
> -            word_size = 4;
> +            fip_width = 4;
>          }
> +        else
> +            fip_width = 8;
>      }
>      else
>      {
>          XSAVE("");
> -        word_size = 4;
>      }
>  #undef XSAVE
> -    if ( word_size >= 0 )
> -        ptr->fpu_sse.x[FPU_WORD_SIZE_OFFSET] = word_size;
> +    ptr->fpu_sse.x[FPU_WORD_SIZE_OFFSET] = fip_width;
>  }

There's actually a pre-existing bug here that I think should get
fixed at once: The 64-bit save path avoided to update
ptr->fpu_sse.x[FPU_WORD_SIZE_OFFSET] when FPU state
didn't get saved (by setting word_size to -1), which continues to be
the case due to patch 1's changes. The 32-bit code path violated
this even before your change. I.e. the last else visible above
should get extended to return when !(mask & XSTATE_FP).

Jan


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