linux-kernel - Re: [PATCH v3 09/10] x86/fpu/xstate: Preserve supervisor states for slow path of __fpu__restore

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Message-ID: <20200510084625.GA19352@zn.tnic>
Date:   Sun, 10 May 2020 10:46:25 +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 09/10] x86/fpu/xstate: Preserve supervisor states for
 slow path of __fpu__restore_sig()

On Sat, Mar 28, 2020 at 09:43:06AM -0700, Yu-cheng Yu wrote:
> The signal return code is responsible for taking an XSAVE buffer present
> in user memory and loading it into the hardware registers.  This
> operation only affects user XSAVE state and never affects supervisor state.
> 
> The fast path through this code simply points XRSTOR directly at the
> user buffer.  However, due to page faults, this XRSTOR can fail.  If it
			 ^^^^^^^^^^^^^^^^^^

"However, since user memory is not guaranteed to be always mapped, ... "

> fails, the signal return code falls back to a slow path which can
> tolerate page faults.
>
> That slow path copies the xfeatures one by one out of the user buffer
> into the task's fpu state area.  However, by being in a context where it
> can handle page faults, the code can also schedule.  That exposes us to
								    ^^
Pls use passive voice in your commit message: no "we" or "I", etc, and
describe your changes in imperative mood.

Fix this in all your commit messages pls.

-- 
Regards/Gruss,
    Boris.

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