linux-kernel - Re: [PATCH v3 05/10] x86/fpu/xstate: Define new functions for clearing fpregs and xstates

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Message-ID: <1b43e3cc36dd707c0268e96b166eca4421d7c2e2.camel@intel.com>
Date:   Wed, 29 Apr 2020 10:02:46 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
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 05/10] x86/fpu/xstate: Define new functions for
 clearing fpregs and xstates

On Wed, 2020-04-29 at 18:39 +0200, Borislav Petkov wrote:
> On Wed, Apr 29, 2020 at 09:06:44AM -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 (e.g. CET xstates)
> > must remain active for signals; 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.
> > 
> > Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> > Co-developed-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> > Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>
> > Reviewed-by: Tony Luck <tony.luck@...el.com>
> > 
> > v3:
> > - Put common code into a static function fpu__clear(), with a parameter
> >   user_only.
> > 
> > v2:
> > - Fixed an issue where fpu__clear_user_states() drops supervisor xstates.
> > - Revise commit log.
> 
> Try applying that patch from this mail yourself and see whether the
> patch changelog will remain in the commit message or it will get
> discarded.

My mistake!  I will fix it.

> 
> > @@ -318,18 +313,40 @@ static inline void copy_init_fpstate_to_fpregs(void)
> >   * Called by sys_execve(), by the signal handler code and by various
> >   * error paths.
> >   */
> > -void fpu__clear(struct fpu *fpu)
> > +static void fpu__clear(struct fpu *fpu, int user_only)
> >  {
> > -	WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */
> > +	WARN_ON_FPU(fpu != &current->thread.fpu);
> 
> Why did you remove the side comment?
> 
> Is it wrong?
> 
> Why do you do such arbitrary changes which are not needed instead of
> concentrating on only the changes the patch should do?

It has been some time since Thomas commented on this tail comment.
https://lore.kernel.org/lkml/alpine.DEB.2.21.1908161703010.1923@nanos.tec.linutronix.de/

I think why not fixing it while at it.

Yu-cheng