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

From: Borislav Petkov <bp@alien8.de>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Tony Luck <tony.luck@intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Rik van Riel <riel@surriel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Fenghua Yu <fenghua.yu@intel.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v3 05/10] x86/fpu/xstate: Define new functions for clearing fpregs and xstates
Date: Wed, 29 Apr 2020 11:27:35 +0200	[thread overview]
Message-ID: <20200429092735.GA16407@zn.tnic> (raw)
In-Reply-To: <20200328164307.17497-6-yu-cheng.yu@intel.com>

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