linux-kernel - Re: [PATCH 3/6] x86/cpu: proc - remove "wp" status line in cpuinfo

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Message-ID: <CA+rthh-KD3DAqnd9Ypv62gAbKrT5TBAx78hQRK8CWH16CbHPgQ@mail.gmail.com>
Date:   Tue, 14 Feb 2017 22:42:31 +0100
From:   Mathias Krause <minipli@...glemail.com>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jesper Nilsson <jesper.nilsson@...s.com>,
        Mikael Starvik <starvik@...s.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        x86-ml <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH 3/6] x86/cpu: proc - remove "wp" status line in cpuinfo

On 14 February 2017 at 19:13, H. Peter Anvin <hpa@...or.com> wrote:
> On 02/12/17 13:12, Mathias Krause wrote:
>> As of commit a5c2a893dbd4 ("x86, 386 removal: Remove
>> CONFIG_X86_WP_WORKS_OK") the kernel won't boot if CR0.WP isn't working
>> correctly. This makes a process reading this file always see "wp : yes"
>> here -- otherwise there would be no process to begin with ;)
>>
>> As this status line in /proc/cpuinfo serves no purpose for quite some
>> time now, get rid of it.
>>
>> Cc: Borislav Petkov <bp@...en8.de>
>> Cc: H. Peter Anvin <hpa@...ux.intel.com>
>> Signed-off-by: Mathias Krause <minipli@...glemail.com>
>> ---
>>  arch/x86/kernel/cpu/proc.c |    6 ++----
>>  1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
>> index 6df621ae62a7..c6c5217a7980 100644
>> --- a/arch/x86/kernel/cpu/proc.c
>> +++ b/arch/x86/kernel/cpu/proc.c
>> @@ -30,8 +30,7 @@ static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
>>                  "coma_bug\t: %s\n"
>>                  "fpu\t\t: %s\n"
>>                  "fpu_exception\t: %s\n"
>> -                "cpuid level\t: %d\n"
>> -                "wp\t\t: yes\n",
>> +                "cpuid level\t: %d\n",
>>                  static_cpu_has_bug(X86_BUG_FDIV) ? "yes" : "no",
>>                  static_cpu_has_bug(X86_BUG_F00F) ? "yes" : "no",
>>                  static_cpu_has_bug(X86_BUG_COMA) ? "yes" : "no",
>> @@ -45,8 +44,7 @@ static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
>>       seq_printf(m,
>>                  "fpu\t\t: yes\n"
>>                  "fpu_exception\t: yes\n"
>> -                "cpuid level\t: %d\n"
>> -                "wp\t\t: yes\n",
>> +                "cpuid level\t: %d\n",
>>                  c->cpuid_level);
>>  }
>>  #endif
>>
>
> Potential userspace breakage, which is why the line was left in the
> first place despite its value now being hard-coded.  Removing it will
> save a whopping 9 bytes of kernel rodata; this is a very small price to
> pay for guaranteeing continued compatibility.

Indeed. That's why I've separated the removal into an extra patch --
to make it easier not to take it.

>
> Nacked-by: H. Peter Anvin <hpa@...or.com>

Do you want me to send the series again without this patch and patch
#6 (Geert took it already) or are you okay with sorting them out
yourself?

Cheers,
Mathias