linux-kernel - Re: [Patch v3 07/13] x86/process Add arch_set

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Date:   Fri, 19 Oct 2018 21:12:48 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
cc:     Jiri Kosina <jikos@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Subject: Re: [Patch v3 07/13] x86/process Add arch_set_dumpable

On Thu, 18 Oct 2018, Tim Chen wrote:
> On 10/18/2018 06:28 AM, Thomas Gleixner wrote:
> > 
> > So now the obvious question. set_dumpable() operates on tsk->mm. i.e. it's
> > a process wide operation. But arch_set_dumpable() operates on the task
> > itself. What about the other tasks of that process?
> 
> I missed this part.
> 
> Fixing this is tricky as I don't see an easy way to
> reverse map mm back to all tasks that use the same mm
> to update their STIBP flags.

task is known and handed in to the function. So why do you want to reverse
map mm?

for_each_thread(task, ...) is what you want. The only thing to verify is
whether you can lock the tasks sighand lock there. And then it's enough to
set/clear the TIF bit and let it take effect at the next context switch.

Thanks,

	tglx