linux-kernel - Re: [PATCH v3 07/10] x86/fpu/xstate: Update copy_kernel_to_xregs

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Date:   Thu, 7 May 2020 15:28:00 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v3 07/10] x86/fpu/xstate: Update
 copy_kernel_to_xregs_err() for XSAVES supervisor states

On Sat, Mar 28, 2020 at 09:43:04AM -0700, Yu-cheng Yu wrote:
> The function copy_kernel_to_xregs_err() uses XRSTOR, which can work with
> standard or compacted format without supervisor xstates.  However, when
> supervisor xstates are present, XRSTORS must be used.  Fix it by using
> XRSTORS when XSAVES is enabled.
> 
> I also considered if there were additional cases where XRSTOR might be
> mistakenly called instead of XRSTORS.  There are only three XRSTOR sites
> in kernel:
> 
> 1. copy_kernel_to_xregs_booting(), already switches between XRSTOR and
>    XRSTORS based on X86_FEATURE_XSAVES.
> 2. copy_user_to_xregs(), which *needs* XRSTOR because it is copying from
>    userspace and must never copy supervisor state with XRSTORS.
> 3. copy_kernel_to_xregs_err() mistakenly used XRSTOR only.  Fixed in
>    this patch.

Avoid having "This patch" or "This commit" in the commit message. It is
tautologically useless.

Also, do

$ git grep 'This patch' Documentation/process

for more details.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette