Re: [Xen-devel] [PATCH] x86/amd: re-enable CPU topology extensions in case BIOS has disabled it

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 30/05/2012 16:04, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> BIOS will switch off the corresponding feature flag on family
> 15h models 10h-1fh non-desktop CPUs.

Why would it do that? It seems silly.

> The topology extension CPUID leafs are required to detect which
> cores belong to the same compute unit. (thread siblings mask is
> set accordingly and also correct information about L1i and L2
> cache sharing depends on this).
> 
> W/o this patch we wouldn't see which cores belong to the same
> compute unit and also cache sharing information for L1i and L2
> would be incorrect on such systems.
> 
> Signed-off-by: Andreas Herrmann <andreas.herrmann3@xxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Assuming there's no good reason for the BIOS having disabled the feature...

Acked-by: Keir Fraser <keir@xxxxxxx>

> --- a/xen/arch/x86/cpu/amd.c
> +++ b/xen/arch/x86/cpu/amd.c
> @@ -471,6 +471,21 @@ static void __devinit init_amd(struct cp
> }
> }
>  
> + /* re-enable TopologyExtensions if switched off by BIOS */
> + if ((c->x86 == 0x15) &&
> +     (c->x86_model >= 0x10) && (c->x86_model <= 0x1f) &&
> +     !cpu_has(c, X86_FEATURE_TOPOEXT) &&
> +     !rdmsr_safe(MSR_K8_EXT_FEATURE_MASK, value)) {
> +  value |= 1ULL << 54;
> +  wrmsr_safe(MSR_K8_EXT_FEATURE_MASK, value);
> +  rdmsrl(MSR_K8_EXT_FEATURE_MASK, value);
> +  if (value & (1ULL << 54)) {
> +   set_bit(X86_FEATURE_TOPOEXT, c->x86_capability);
> +   printk(KERN_INFO "CPU: Re-enabling disabled "
> +          "Topology Extensions Support\n");
> +  }
> + }
> +
>          amd_get_topology(c);
>  
> /* Pointless to use MWAIT on Family10 as it does not deep sleep. */
> 
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel