linux-kernel - Re: [PATCH 1/6] x86: drop unneded members of struct cpuinfo

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Date:   Tue, 14 Feb 2017 17:40:40 +0100
From:   Mathias Krause <minipli@...glemail.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "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 1/6] x86: drop unneded members of struct cpuinfo_x86

On 14 February 2017 at 17:17, Borislav Petkov <bp@...en8.de> wrote:
> On Sun, Feb 12, 2017 at 10:12:07PM +0100, Mathias Krause wrote:
>> Those member serve no purpose -- not even fill padding for alignment or
>> such. So just get rid of them.
>
> Well, almost. You need the wp_works_ok removal patch too, otherwise you
> have the 3 bytes hole below.

Heh, indeed! But only since commit 79a8b9aa388b ("x86/CPU/AMD: Bring
back Compute Unit ID") ;)

> But the wp_works_ok goes away too so I guess that's fine.
>
> $ pahole -C cpuinfo_x86 vmlinux
> struct cpuinfo_x86 {
>         __u8                       x86;                  /*     0     1 */
>         __u8                       x86_vendor;           /*     1     1 */
>         __u8                       x86_model;            /*     2     1 */
>         __u8                       x86_mask;             /*     3     1 */
>         char                       wp_works_ok;          /*     4     1 */
>         __u8                       x86_virt_bits;        /*     5     1 */
>         __u8                       x86_phys_bits;        /*     6     1 */
>         __u8                       x86_coreid_bits;      /*     7     1 */
>         __u8                       cu_id;                /*     8     1 */
>
>         /* XXX 3 bytes hole, try to pack */

The cu_id member is "new". Without it there would be no hole. But,
yeah, without wp_works_ok everything's fine again.

Cheers,
Mathias