Re: [PATCH v4 04/17] x86/split_lock: Align x86_capability to unsigned long to avoid split locked access

Peter Zijlstra
2019-03-04T20:12:01Z

On Mon, Mar 04, 2019 at 10:52:19AM -0800, Dave Hansen wrote:
> On 3/1/19 6:44 PM, Fenghua Yu wrote:
> > diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> > index 33051436c864..eb8ae701ef65 100644
> > --- a/arch/x86/include/asm/processor.h
> > +++ b/arch/x86/include/asm/processor.h
> > @@ -93,7 +93,9 @@ struct cpuinfo_x86 {
> > __u32 extended_cpuid_level;
> > /* Maximum supported CPUID level, -1=no CPUID: */
> > int cpuid_level;
> > - __u32 x86_capability[NCAPINTS + NBUGINTS];
> > + /* Unsigned long alignment to avoid split lock in atomic bitmap ops */
> > + __u32 x86_capability[NCAPINTS + NBUGINTS]
> > + __aligned(sizeof(unsigned long));
>
> I think this also warrants a comment in the changelog about the
> alignment of 'struct cpuinfo_x86'.

Nah.