linux-kernel - Re: [patch 20/24] x86/speculation: Split out TIF update

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Message-ID: <alpine.DEB.2.21.1811230000590.1665@nanos.tec.linutronix.de>
Date:   Fri, 23 Nov 2018 00:04:22 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ingo Molnar <mingo@...nel.org>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Casey Schaufler <casey.schaufler@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jon Masters <jcm@...hat.com>,
        Waiman Long <longman9394@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Dave Stewart <david.c.stewart@...el.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [patch 20/24] x86/speculation: Split out TIF update

On Thu, 22 Nov 2018, Ingo Molnar wrote:
> * Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> Had to read this twice, because the comment and the code are both correct 
> but deal with the inverse case. This might have helped:
> 
> 	/*
> 	 * Immediately update the speculation MSRs on the current task,
> 	 * but for non-current tasks delay setting the CPU mitigation 
> 	 * until it is scheduled next.
> 	 */
> 	if (tsk == current && update)
> 		speculation_ctrl_update_current();
> 
> But can the target task ever be non-current here? I don't think so: the 
> two callers are prctl and seccomp, and both are passing in the current 
> task pointer.

See te other mail. Yes, seccomp passes non current task pointers. Will
update the comment.

Thanks,

	tglx