Re: [PATCH CPU v1] cpuid: initialize cpuinfo with boot_cpu_data

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Feb 11, 2022 at 11:50:46AM +0100, Jan Beulich wrote:
> On 11.02.2022 11:47, Roger Pau Monné wrote:
> > On Fri, Feb 11, 2022 at 11:32:45AM +0100, Jan Beulich wrote:
> >> On 11.02.2022 10:02, Roger Pau Monné wrote:
> >>> On Fri, Feb 11, 2022 at 08:23:27AM +0100, Norbert Manthey wrote:
> >>>> When re-identifying CPU data, we might use uninitialized data when
> >>>> checking for the cache line property to adapt the cache
> >>>> alignment. The data that depends on this uninitialized read is
> >>>> currently not forwarded.
> >>>>
> >>>> To avoid problems in the future, initialize the data cpuinfo
> >>>> structure before re-identifying the CPU again.
> >>>>
> >>>> The trace to hit the uninitialized read reported by Coverity is:
> >>>>
> >>>> bool recheck_cpu_features(unsigned int cpu)
> >>>> ...
> >>>>     struct cpuinfo_x86 c;
> >>>>     ...
> >>>>     identify_cpu(&c);
> >>>>
> >>>> void identify_cpu(struct cpuinfo_x86 *c)
> >>>> ...
> >>>>     generic_identify(c)
> >>>>
> >>>> static void generic_identify(struct cpuinfo_x86 *c)
> >>>> ...
> >>>
> >>> Would it be more appropriate for generic_identify to also set
> >>> x86_cache_alignment like it's done in early_cpu_init?
> >>>
> >>> generic_identify already re-fetches a bunch of stuff that's also
> >>> set by early_cpu_init for the BSP.
> >>
> >> This would be an option, but how sure are you that there isn't
> >> (going to be) another field with similar properties? We better
> >> wouldn't require _everything_ to be re-filled in generic_identify().
> > 
> > So you think generic_identify should call into early_cpu_init, or even
> > split the cpuinfo_x86 filling done in early_cpu_init into a non-init
> > function that could be called by both generic_identify and
> > early_cpu_init?
> 
> No, I think it is quite fine for this to be a two-step process.

But it's not a two step process for all CPUs. It's a two step process
for the BSP, that will get it's cpuinfo filled by early_cpu_init
first, and then by identify_cpu. OTHO APs will only get the
information filled by identify_cpu.

Maybe APs don't care about having x86_cache_alignment correctly set?

Thanks, Roger.