linux-kernel - Re: [RFC PATCH] perf/x86/intel/rapl: avoid access unallocate memory

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Message-ID: <alpine.DEB.2.20.1611081721330.3501@nanos>
Date:   Tue, 8 Nov 2016 17:22:09 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Charles (Chas) Williams" <ciwillia@...cade.com>
cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org, "M. Vefa Bicakci" <m.v.b@...box.com>
Subject: Re: [RFC PATCH] perf/x86/intel/rapl: avoid access unallocate
 memory

On Tue, 8 Nov 2016, Charles (Chas) Williams wrote:
> On 11/08/2016 09:31 AM, Thomas Gleixner wrote:
> > On Tue, 8 Nov 2016, Charles (Chas) Williams wrote:
> > > 	[    0.016335] topology_update_package_map:  apicid 0  pkg 0  cpu 0
> > > 	[    0.016398] smpboot: APIC(0) Converting physical 0 to logical
> > > package 0, cpu 0 (ffff88023fc0a040)
> > > 	[    0.016399] topology_update_package_map:  apicid 1  pkg 1  cpu 1
> > > 	[    0.016462] smpboot: APIC(1) Converting physical 1 to logical
> > > package 1, cpu 1 (ffff88023fd0a040)
> > > 
> > > So, I don't know where apic->cpu_present_to_apicid(cpu) is getting its
> > > apicid but it certainly doesn't seem to the match the apicid in the
> > > CPU's registers.  For whatever reason, my VMware system is reporting
> > > that the second CPU has a local APIC ID of 2:
> > 
> > The initial information comes from MP tables or ACPI.
> > 
> > > 	[    0.009115] identify_cpu: cpu_index 0  phys_proc_id is now 0,
> > > apicid 0, initial_apicid 0
> > > 	...
> > > 	[    0.237401] identify_cpu: cpu_index 1  phys_proc_id is now 2,
> > > apicid 2, initial_apicid 2
> > 
> > And the CPUID emulation tells something different. Sigh!
> > 
> > > I was thinking it might be better to call topology_update_package_map()
> > > at the bottom of identify_cpu() to setup the secondary CPU's.  The boot
> > > cpu could be setup during smp_init_package_map().
> > 
> > Perhaps, but that does not make the inconsistencies go away....
> 
> By the time I know it's not consistent, there isn't anything I can do
> about it.  I can't update the table to remove the bad information.
> 
> The other alternative, is to trust the ACPI and just update the
> cpu_data's apicid in identify_cpu() to the value from the table.
> The earlier kernels didn't seem to rely as much on this information.
> But it does appear to be "wrong" in the APIC table.  From acpidump:
> 
> [02Ch 0044   1]                Subtable Type : 00 [Processor Local APIC]
> [02Dh 0045   1]                       Length : 08
> [02Eh 0046   1]                 Processor ID : 00
> [02Fh 0047   1]                Local Apic ID : 00
> [030h 0048   4]        Flags (decoded below) : 00000001
>                            Processor Enabled : 1
> 
> [034h 0052   1]                Subtable Type : 00 [Processor Local APIC]
> [035h 0053   1]                       Length : 08
> [036h 0054   1]                 Processor ID : 01
> [037h 0055   1]                Local Apic ID : 01
> [038h 0056   4]        Flags (decoded below) : 00000001
>                            Processor Enabled : 1

Well, which one is wrong is hard to tell :)

I'll have a look how to sort that out.

Thanks,

	tglx