Re: [Xen-devel] [PATCH v3 09/11] x86/xen: use capabilities instead of fake cpuid values for xsave

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

> +static bool __init xen_check_xsave(void)
>  {
> -     unsigned int ax, bx, cx, dx;
> -     unsigned int xsave_mask;
> +     unsigned int err, eax, edx;
>  
> -     ax = 1;
> -     cx = 0;
> -     cpuid(1, &ax, &bx, &cx, &dx);
> +     /* Test OSXSAVE capability via xgetbv instruction. */
> +     asm volatile("1: .byte 0x0f,0x01,0xd0\n\t" /* xgetbv */
> +                  "xor %[err], %[err]\n"
> +                  "2:\n\t"
> +                  ".pushsection .fixup,\"ax\"\n\t"
> +                  "3: movl $1,%[err]\n\t"
> +                  "jmp 2b\n\t"
> +                  ".popsection\n\t"
> +                  _ASM_EXTABLE(1b, 3b)
> +                  : [err] "=r" (err), "=a" (eax), "=d" (edx)
> +                  : "c" (0));

Have you tested this on processors where we actually trap on xgetbv?

I have an AMD box without XSAVE support and this is a fatal error. I
suspect it's too early to use exception fixup framework here.

-boris



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