linux-kernel - Re: [PATCH] x86, cpuinfo fix cpu_data(0) x86_model

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Message-ID: <CAMzpN2joER5N_Ud5hRh31yahHdjgSsjv0F_Sw8vzyg02x1oaZA@mail.gmail.com>
Date:	Mon, 18 May 2015 16:27:02 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Prarit Bhargava <prarit@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>,
	Igor Mammedov <imammedo@...hat.com>,
	Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH] x86, cpuinfo fix cpu_data(0) x86_model_id field truncation

On Mon, May 18, 2015 at 3:45 PM, Borislav Petkov <bp@...en8.de> wrote:
> On Mon, May 18, 2015 at 02:21:00PM -0400, Prarit Bhargava wrote:
>> When comparing 'model name' fields in /proc/cpuinfo it was noticed that
>> a simple test comparing the model name fields was failing.  After some
>> simple investigation it was noticed that, in fact, the model name fields
>> are different for each processor.  Processor 0's model name field had
>> white space removed, while the other processors did not.
>>
>> Another way of seeing this behaviour is to convert spaces into underscores
>> in the output of /proc/cpuinfo,
>>
>> [thetango@...rit ~]# grep "^model name" /proc/cpuinfo | uniq -c | sed 's/\ /_/g'
>> ______1_model_name      :_AMD_Opteron(TM)_Processor_6272
>> _____63_model_name      :_AMD_Opteron(TM)_Processor_6272_________________
>>
>> which shows two different model name fields even though they should be the
>> same.
>>
>> This occurs because the kernel calls strim() on cpu 0's x86_model_id field
>
> I'd actually prefer this much simpler patch:
>
> ---
> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> index e7d8c7608471..d215e9b26567 100644
> --- a/arch/x86/kernel/cpu/proc.c
> +++ b/arch/x86/kernel/cpu/proc.c
> @@ -67,7 +67,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>                    c->x86_vendor_id[0] ? c->x86_vendor_id : "unknown",
>                    c->x86,
>                    c->x86_model,
> -                  c->x86_model_id[0] ? c->x86_model_id : "unknown");
> +                  c->x86_model_id[0] ? strim(c->x86_model_id) : "unknown");
>
>         if (c->x86_mask || c->cpuid_level >= 0)
>                 seq_printf(m, "stepping\t: %d\n", c->x86_mask);

The problem here is that strim() modifies the string in place,
replacing the first trailing space with a null.  I think the best
solution is to do the trimming in get_model_name().  It already trims
leading spaces for Intel.

--
Brian Gerst
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