linux-kernel - Re: [RFC PATCH v2 09/18] livepatch/x86: add TIF_PATCH

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Message-ID: <20160429201822.rj5hbkfkjgrdxlz6@treble>
Date:	Fri, 29 Apr 2016 15:18:22 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Jessica Yu <jeyu@...hat.com>, Jiri Kosina <jikos@...nel.org>,
	Miroslav Benes <mbenes@...e.cz>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	live-patching@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, linuxppc-dev@...ts.ozlabs.org,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	Vojtech Pavlik <vojtech@...e.com>, Jiri Slaby <jslaby@...e.cz>,
	Petr Mladek <pmladek@...e.com>,
	Chris J Arges <chris.j.arges@...onical.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [RFC PATCH v2 09/18] livepatch/x86: add TIF_PATCH_PENDING thread
 flag

On Fri, Apr 29, 2016 at 11:08:04AM -0700, Andy Lutomirski wrote:
> On Thu, Apr 28, 2016 at 1:44 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > Add the TIF_PATCH_PENDING thread flag to enable the new livepatch
> > per-task consistency model for x86_64.  The bit getting set indicates
> > the thread has a pending patch which needs to be applied when the thread
> > exits the kernel.
> >
> > The bit is placed in the least-significant word of the thread_info flags
> 
> NAK to that part.
> 
> The least-significant word thing is a huge hack that has gotten out of
> control.  Please add the thing explicitly to all relevant masks.

Yeah, it is quite dangerous.  I'll make it explicit, and make all the
other _TIF_ALLWORK_MASK flags explicit while I'm at it.

-- 
Josh