linux-kernel - Re: [PATCH v3 45/51] x86: remove 64-byte gap at end of irq stack

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Message-ID: <CALCETrXYVYuz+SEfXacjojA8bShWZaMafSqJaGTPqZ2adDv+EQ@mail.gmail.com>
Date:	Sun, 14 Aug 2016 00:52:40 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H . Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Brian Gerst <brgerst@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Byungchul Park <byungchul.park@....com>,
	Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH v3 45/51] x86: remove 64-byte gap at end of irq stack

On Fri, Aug 12, 2016 at 7:29 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> There has been a 64-byte gap at the end of the irq stack for at least 12
> years.  It predates git history, and I can't find any good reason for
> it.  Remove it.  What's the worst that could happen?

I can't think of any reason this would matter.

For that matter, do you have any idea why irq_stack_union is a union
or why we insist on sticking it at %gs:0?  Sure, the *canary* needs to
live at a fixed offset (because GCC is daft, sigh), but I don't see
what that has to do with the rest of the IRQ stack.

--Andy