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

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Message-ID: <e3a6f9cb-ee46-6e5c-7b2e-9a6ed2fc949e@brocade.com>
Date:   Tue, 8 Nov 2016 09:20:52 -0500
From:   "Charles (Chas) Williams" <ciwillia@...cade.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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 11/07/2016 03:20 PM, Thomas Gleixner wrote:
> On Mon, 7 Nov 2016, Charles (Chas) Williams wrote:
>> On 11/07/2016 11:19 AM, Thomas Gleixner wrote:
>>> On Wed, 2 Nov 2016, Charles (Chas) Williams wrote:
>>>> I don't know why the CPU's phys_proc_id is 2.
>>>
>>> max_physical_pkg_id gets initialized via:
>>>
>>>     cpus = boot_cpu_data.x86_max_cores;
>>>     max_physical_pkg_id = DIV_ROUND_UP(MAX_LOCAL_APIC, ncpus);
>>>
>>> What's the value of boot_cpu_data.x86_max_cores and MAX_LOCAL_APIC?
>>
>> I have discovered that that is not the problem.  smp_init_package_map()
>> is calculating the physical core id using the following:
>>
>>         for_each_present_cpu(cpu) {
>>                 unsigned int apicid = apic->cpu_present_to_apicid(cpu);
>>
>> 		...
>> 		if (!topology_update_package_map(apicid, cpu))
>>                         continue;
>>
>> 	...
>> 	int topology_update_package_map(unsigned int apicid, unsigned int cpu)
>> 	{
>> 		unsigned int new, pkg = apicid >>
>> boot_cpu_data.x86_coreid_bits;
>>
>> But later when the secondary CPU's are identified they use a different
>> calculation using the local APIC ID from the CPU's registers:
>>
>> 	static void generic_identify(struct cpuinfo_x86 *c)
>> 	...
>>         if (c->cpuid_level >= 0x00000001) {
>>                 c->initial_apicid = (cpuid_ebx(1) >> 24) & 0xFF;
>> 	...
>> 		c->phys_proc_id = c->initial_apicid;
>>
>> So at the end of identify_cpu() when the boot/hotplug assignment is
>> put back:
>>
>>         c->logical_proc_id = topology_phys_to_logical_pkg(c->phys_proc_id);
>>
>> topology_phys_to_logical_pkg() is returning an invalid logical processor
>> since one isn't configured.
>>
>> It's not clear to me what the right thing to do is or which is right.
>
> Nice detective work! So the issue is that the package mapping code honours
> boot_cpu_data.x86_coreid_bit, while generic_identify does
> not. boot_cpu_data.x86_coreid_bit is obviously 1 in your case. Tentative
> fix below. I still need to gow through that maze and figure out what could
> go wrong with that :(

I don't think that will fix the issue.  My deubugging leads me to believe
that boot_cpu_data.x86_coreid_bits is probably 0:

	[    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:

	[    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

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().

topology_update_package_map() is also poorly named it can create the
assignment, but can't update it (since it doesn't know the previous
mapping).


> 8<------------------------
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -905,6 +905,8 @@ static void detect_null_seg_behavior(str
>
>  static void generic_identify(struct cpuinfo_x86 *c)
>  {
> +	unsigned int pkg;
> +
>  	c->extended_cpuid_level = 0;
>
>  	if (!have_cpuid_p())
> @@ -929,7 +931,8 @@ static void generic_identify(struct cpui
>  		c->apicid = c->initial_apicid;
>  # endif
>  #endif
> -		c->phys_proc_id = c->initial_apicid;
> +		pkg = c->initial_apicid >> boot_cpu_data.x86_coreid_bits;
> +		c->phys_proc_id = pkg;
>  	}
>
>  	get_model_name(c); /* Default name */
>
>
>