linux-kernel - Re: [PATCH 5/6] x86/fpu/xstate: Define new functions for clearing fpregs and xstates

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Message-ID: <20191009172804.GI10395@zn.tnic>
Date:   Wed, 9 Oct 2019 19:28:04 +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 5/6] x86/fpu/xstate: Define new functions for clearing
 fpregs and xstates

On Wed, Sep 25, 2019 at 08:10:21AM -0700, Yu-cheng Yu wrote:
> From: Fenghua Yu <fenghua.yu@...el.com>
> 
> Currently, fpu__clear() clears all fpregs and xstates.  Once XSAVES
> supervisor states are introduced, supervisor settings must remain active
> for signals;

I could very well use an example here: for signal handling supervisor
states, I'm guessing this would be something CET-related so some text
about a usage scenario would be very helpful here.

> it is necessary to have separate functions:
> 
>  - Create fpu__clear_user_states(): clear only user settings for signals;
>  - Create fpu__clear_all(): clear both user and supervisor settings in
>    flush_thread().
> 
> Also modify copy_init_fpstate_to_fpregs() to take a mask from above two
> functions.
> 
> Co-developed-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>

As before...

-- 
Regards/Gruss,
    Boris.

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