linux-kernel - Re: [PATCH 3/3] x86/mce: Use mce_prep_record() helpers for apei_smca_report_x86

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Date: Tue, 18 Jun 2024 11:11:51 -0400
From: Yazen Ghannam <yazen.ghannam@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
	tony.luck@...el.com, x86@...nel.org, avadhut.naik@....com,
	john.allen@....com
Subject: Re: [PATCH 3/3] x86/mce: Use mce_prep_record() helpers for
 apei_smca_report_x86_error()

On Sat, Jun 15, 2024 at 12:44:20AM +0200, Borislav Petkov wrote:
> On Fri, Jun 14, 2024 at 05:47:36PM -0400, Yazen Ghannam wrote:
> > I don't see why it won't work. If there is no break, then the iterator
> > ends by setting the variable past the last valid value.
> > 
> > For example, I ran this on a system with 512 CPUs:
> > 
> >         unsigned int cpu;
> > 
> > 	/* Loops over CPUs 0-511. */
> >         for_each_possible_cpu(cpu)
> >                 pr_info("loop: cpu=%d\n", cpu);
> > 
> > 	/* CPU is now set to 512. */
> >         pr_info("final: cpu=%d\n", cpu);
> > 
> > 	/* CPU 512 is not possible. */
> >         pr_info("CPU %d is %s possible\n", cpu, cpu_possible(cpu) ? "" : "not");
> > 
> > But...I like your suggestion as it is much more explicit. And I might be
> > missing something. :/
> 
> I can think of at least three:
> 
> * CPU topology and the initial_apicid sometimes can get programmed wrong by the
> * FW. Nothing new.
> 
> * nr_cpus= - you can enable less CPUs than actually physically present so an MCE
> on a CPU which is not enabled by Linux will be -EINVAL
> 
> * possible_cpus= - pretty much the same thing
> 
> But I haven't actually tried them - am just looking at the code.
> 
> And yes, with the apicid_found boolean it is perfectly clear what's going on.
> 
> And looking at
> 
>   convert_apicid_to_cpu()
> 
> which already does that loop, we probably should talk to tglx whether we can
> simply export that helper.
> 
> And better yet if he's done some more helpful caching of the reverse mapping:
> apicid to CPU number. As part of the topology rewrite. Because then we don't
> need the loop at all.
>

Agreed. Here's another option: topo_lookup_cpuid()

Thanks,
Yazen