Re: [Xen-devel] [PATCH] tools/libxc: Correct use of X86_XSS_MASK in guest xstate generation

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Apr 19, 2016 at 06:27:05PM +0100, Andrew Cooper wrote:
> c/s 75f9455e "tools/libxc: Calculate xstate cpuid leaf from guest information"
> incorrectly inverted the shift and mask when using X86_XSS_MASK.  Luckily, the
> mask is currently zero, avoiding incorrect calculations.
> 
> While adjusting this, use an explcit uint32_t cast rather than masking against
> 0xffffffff.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> 
> Submitted-from: A punt, on the Cam, during the the hackathon, because.


Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
Release-acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

On a punt, too, because

> ---
>  tools/libxc/xc_cpuid_x86.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
> index 6d14904..84f4e08 100644
> --- a/tools/libxc/xc_cpuid_x86.c
> +++ b/tools/libxc/xc_cpuid_x86.c
> @@ -460,7 +460,7 @@ static void xc_cpuid_config_xsave(xc_interface *xch,
>      {
>      case 0:
>          /* EAX: low 32bits of xfeature_enabled_mask */
> -        regs[0] = guest_xfeature_mask & 0xFFFFFFFF;
> +        regs[0] = (uint32_t)guest_xfeature_mask;
>          /* EDX: high 32bits of xfeature_enabled_mask */
>          regs[3] = guest_xfeature_mask >> 32;
>          /* ECX: max size required by all HW features */
> @@ -487,8 +487,8 @@ static void xc_cpuid_config_xsave(xc_interface *xch,
>  
>          if ( test_bit(X86_FEATURE_XSAVES, info->featureset) )
>          {
> -            regs[2] = guest_xfeature_mask & X86_XSS_MASK & 0xFFFFFFFF;
> -            regs[3] = (guest_xfeature_mask >> 32) & X86_XSS_MASK;
> +            regs[2] = (uint32_t)(guest_xfeature_mask & X86_XSS_MASK);
> +            regs[3] = (guest_xfeature_mask & X86_XSS_MASK) >> 32;
>          }
>          else
>              regs[2] = regs[3] = 0;
> -- 
> 1.9.1
> 

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