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

[Fenghua Yu]

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'.

How about add "Depending on the starting address where GCC generates
for data of struct cpuinfo_x86, x86_capability[] may or may not align to
unsigned long...."?

Thanks.

-Fenghua