Re: [Xen-devel] [PATCH v3 07/18] x86emul: support {,V}{LD,ST}MXCSR

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 15/02/17 11:11, Jan Beulich wrote:
> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -6183,6 +6200,23 @@ x86_emulate(
>      case X86EMUL_OPC(0x0f, 0xae): case X86EMUL_OPC_66(0x0f, 0xae): /* Grp15 
> */
>          switch ( modrm_reg & 7 )
>          {
> +        case 2: /* ldmxcsr */
> +            generate_exception_if(vex.pfx, EXC_UD);
> +            vcpu_must_have(sse);
> +        ldmxcsr:
> +            generate_exception_if(src.type != OP_MEM, EXC_UD);
> +            generate_exception_if(src.val & ~mxcsr_mask, EXC_GP, 0);
> +            asm volatile ( "ldmxcsr %0" :: "m" (src.val) );
> +            break;
> +
> +        case 3: /* stmxcsr */
> +            generate_exception_if(vex.pfx, EXC_UD);
> +            vcpu_must_have(sse);
> +        stmxcsr:
> +            generate_exception_if(dst.type != OP_MEM, EXC_UD);
> +            asm volatile ( "stmxcsr %0" : "=m" (dst.val) );
> +            break;
> +
>          case 5: /* lfence */
>              fail_if(modrm_mod != 3);
>              generate_exception_if(vex.pfx, EXC_UD);
> @@ -6226,6 +6260,20 @@ x86_emulate(
>          }
>          break;
>  
> +    case X86EMUL_OPC_VEX(0x0f, 0xae): /* Grp15 */
> +        switch ( modrm_reg & 7 )
> +        {
> +        case 2: /* vldmxcsr */
> +            generate_exception_if(vex.l || vex.reg != 0xf, EXC_UD);
> +            host_and_vcpu_must_have(avx);

If you move the {ld,st}mxcsr labels up by one, these can reduce to just
vcpu_must_have(avx), as we don't use the VEX encoded variant.

Having said that, shouldn't the pfx check be included even in the
VEX-encoded case?  (i.e. the lables move up once again).

~Andrew

> +            goto ldmxcsr;
> +        case 3: /* vstmxcsr */
> +            generate_exception_if(vex.l || vex.reg != 0xf, EXC_UD);
> +            host_and_vcpu_must_have(avx);
> +            goto stmxcsr;
> +        }
> +        goto cannot_emulate;
> +
>      case X86EMUL_OPC_F3(0x0f, 0xae): /* Grp15 */
>          fail_if(modrm_mod != 3);
>          generate_exception_if((modrm_reg & 4) || !mode_64bit(), EXC_UD);
>


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