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

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Message-ID: <20200429092735.GA16407@zn.tnic>
Date:   Wed, 29 Apr 2020 11:27:35 +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 05/10] x86/fpu/xstate: Define new functions for
 clearing fpregs and xstates

On Sat, Mar 28, 2020 at 09:43:02AM -0700, Yu-cheng Yu wrote:
> @@ -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 clear_user_only)

I said:

"fpu__clear(struct fpu *fpu, bool user_only)"
			     ^^^^^^^^^^^^^^

you made it

		     ..., int clear_user_only)

Why?

If you agree with the review comment, then please do it as suggested. If
you don't, then say why you don't.

Why would you do something in-between?

>  {
> -	WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */

Why are you moving this into the callers when *both* do it?

> +	if (static_cpu_has(X86_FEATURE_FPU)) {

Flip this logic:

	if (!static_cpu_has(X86_FEATURE_FPU)) {
                fpu__drop(fpu);
                fpu__initialize(fpu);
		return;
	}

	fpregs_lock();
	...

to save an indentation level and make the important case more readable
and locking more prominent.

-- 
Regards/Gruss,
    Boris.

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