Re: [Xen-devel] [PATCH V3 4/6] libxc: expose xsaves/xgetbv1/xsavec to hvm guest

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2015-08-05 at 09:57 +0800, Shuai Ruan wrote:
> This patch exposes xsaves/xgetbv1/xsavec to hvm guest.
> The reserved bits of eax/ebx/ecx/edx must be cleaned up
> when call cpuid(0dh) with leaf 1 or 2..63.
> 
> According to the spec the following bits must be reseved:

"reserved"

> For leaf 1, bits 03-04/08-31 of ecx is reserved. Edx is reserved.
> For leaf 2...63, bits 01-31 of ecx is reserved. Edx is reserved.
> 
> Signed-off-by: Shuai Ruan <shuai.ruan@xxxxxxxxxxxxxxx>

Although this is toolstack code I think this really ought to be acked by
the hypervisor x86 maintainers, if they are happy with it then I am too,
and in that case you may add:

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

> ---
>  tools/libxc/xc_cpuid_x86.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
> index c97f91a..b69676a 100644
> --- a/tools/libxc/xc_cpuid_x86.c
> +++ b/tools/libxc/xc_cpuid_x86.c
> @@ -211,6 +211,9 @@ static void intel_xc_cpuid_policy(
>  }
>  
>  #define XSAVEOPT        (1 << 0)
> +#define XSAVEC          (1 << 1)
> +#define XGETBV1         (1 << 2)
> +#define XSAVES          (1 << 3)
>  /* Configure extended state enumeration leaves (0x0000000D for xsave) */
>  static void xc_cpuid_config_xsave(
>      xc_interface *xch, domid_t domid, uint64_t xfeature_mask,
> @@ -247,8 +250,9 @@ static void xc_cpuid_config_xsave(
>          regs[1] = 512 + 64; /* FP/SSE + XSAVE.HEADER */
>          break;
>      case 1: /* leaf 1 */
> -        regs[0] &= XSAVEOPT;
> -        regs[1] = regs[2] = regs[3] = 0;
> +        regs[0] &= (XSAVEOPT | XSAVEC | XGETBV1 | XSAVES);
> +        regs[2] &= 0xe7;
> +        regs[3] = 0;
>          break;
>      case 2 ... 63: /* sub-leaves */
>          if ( !(xfeature_mask & (1ULL << input[1])) )
> @@ -256,8 +260,9 @@ static void xc_cpuid_config_xsave(
>              regs[0] = regs[1] = regs[2] = regs[3] = 0;
>              break;
>          }
> -        /* Don't touch EAX, EBX. Also cleanup ECX and EDX */
> -        regs[2] = regs[3] = 0;
> +        /* Don't touch EAX, EBX. Also cleanup EDX. Cleanup bits 01-32 of 
> ECX*/
> +        regs[2] &= 0x1;
> +        regs[3] = 0;
>          break;
>      }
>  }

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