Re: [Xen-devel] [Patch] Disallow SMEP for PV guest

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Jun 01, 2011 at 10:31:12PM +0800, Yang, Wei Y wrote:
> This patch disallows SMEP for PV guest.

What are the reasons for it? What do we gain from it?
> 
>  Signed-off-by: Yang, Wei <wei.y.yang@xxxxxxxxx>
>  Signed-off-by: Shan, Haitao <haitao.shan@xxxxxxxxx>
>  Signed-off-by: Li, Xin <xin.li@xxxxxxxxx>
> 
> ---
>  xc_cpufeature.h |    3 +++
>  xc_cpuid_x86.c  |    5 +++++
>  2 files changed, 8 insertions(+)
> 
> diff -r 6f72160d2d55 tools/libxc/xc_cpufeature.h
> --- a/tools/libxc/xc_cpufeature.h     Wed Jun 01 19:57:32 2011 +0800
> +++ b/tools/libxc/xc_cpufeature.h     Wed Jun 01 22:21:33 2011 +0800
> @@ -141,4 +141,7 @@
>  #define X86_FEATURE_TBM         (6*32+21) /* trailing bit manipulations */
>  #define X86_FEATURE_TOPOEXT     (6*32+22) /* topology extensions CPUID leafs 
> */
>  
> +/* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 7 */
> +#define X86_FEATURE_SMEP       (7*32+ 7) /* Supervisor Mode Execution 
> Protection */
> +
>  #endif /* __LIBXC_CPUFEATURE_H */
> diff -r 6f72160d2d55 tools/libxc/xc_cpuid_x86.c
> --- a/tools/libxc/xc_cpuid_x86.c      Wed Jun 01 19:57:32 2011 +0800
> +++ b/tools/libxc/xc_cpuid_x86.c      Wed Jun 01 22:21:33 2011 +0800
> @@ -470,6 +470,11 @@
>          xc_cpuid_config_xsave(xch, domid, xfeature_mask, input, regs);
>          break;
>  
> +    case 7:
> +        if ( input[1] == 0 )
> +            clear_bit(X86_FEATURE_SMEP, regs[1]);
> +        break;
> +
>      case 0x80000001:
>          if ( !guest_64bit )
>          {
> 
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