Re: [Xen-devel] [PATCH] x86/AMD: Do not enable ARAT feature on AMD processors below family 0x12

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.10.11 at 20:59, Boris Ostrovsky <boris.ostrovsky@xxxxxxx> wrote:
> # HG changeset patch
> # User Boris Ostrovsky <boris.ostrovsky@xxxxxxx>
> # Date 1317915395 14400
> # Node ID 4374a261682e78d6bbf3b3fefb1e779b7a1fc3b3
> # Parent  0b66e6450ffe6823d8b323ef4248b38fe7372d54
> x86/AMD: Do not enable ARAT feature on AMD processors below family 0x12
> 
> Determining whether an AMD processor is affected by erratum 400 may
> have some corner cases and handling these cases is somewhat complicated.
> In the interest of simplicity we won't claim ARAT support on processor
> families below 0x12.
> 
> Mirrors Linux commit e9cdd343a5e42c43bcda01e609fa23089e026470
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxx>
> 
> diff -r 0b66e6450ffe -r 4374a261682e xen/arch/x86/cpu/amd.c
> --- a/xen/arch/x86/cpu/amd.c  Tue Oct 04 14:18:30 2011 +0200
> +++ b/xen/arch/x86/cpu/amd.c  Thu Oct 06 11:36:35 2011 -0400
> @@ -495,8 +495,11 @@
>       }
>  #endif
>  
> -     /* As a rule processors have APIC timer running in deep C states */
> -     if (c->x86 > 0xf && !cpu_has_amd_erratum(c, AMD_ERRATUM_400))
> +     /*
> +      * Family 0x12 and above processors have APIC timer
> +      * running in deep C states.
> +      */
> +     if (c->x86 > 0x11)
>               set_bit(X86_FEATURE_ARAT, c->x86_capability);
>  
>       if (cpuid_edx(0x80000007) & (1 << 10)) {

Applied, but - couldn't we do away with the erratum 400 definition
now? Or is it reasonable to expect that something else could depend
on this (which, following the back-and-forth here, seems to be fuzzy
anyway)? (I wouldn't mind keeping record of it in the example part
of the comment preceding the errata definitions, as is already the
case.)

Jan


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