linux-kernel - Re: [PATCH 1/7] x86/fpu: Simplify the fpu->last_cpu logic and rename it to fpu->fpregs

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Date:   Thu, 26 Jan 2017 09:23:56 -0500
From:   Rik van Riel <riel@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH 1/7] x86/fpu: Simplify the fpu->last_cpu logic and
 rename it to fpu->fpregs_cached

On Thu, 2017-01-26 at 12:26 +0100, Ingo Molnar wrote:
> 
> @@ -322,6 +308,16 @@ struct fpu {
>  	unsigned char			fpregs_active;
>  
>  	/*
> +	 * @fpregs_cached:
> +	 *
> +	 * This flag tells us whether this context is loaded into a
> CPU
> +	 * right now.

Not quite. You are still checking against fpu_fpregs_owner_ctx.

How about something like

      * This flag tells us whether this context was loaded into
      * its current CPU; fpu_fpregs_owner_ctx will tell us whether
      * this context is actually in the registers.

> +	 *
> +	 * This is set to 0 if a task is migrated to another CPU.
> +	 */
> +	unsigned char			fpregs_cached;
> +
> +	/*
>  	 * @state:
>  	 *
>  	 * In-memory copy of all FPU registers that we save/restore