linux-kernel - Re: [PATCH v2 03/44] x86/asm/head: rename 'stack_start' -> 'initial

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Date:	Sat, 6 Aug 2016 08:13:33 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Nilay Vaish <nilayvaish@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H . Peter Anvin" <hpa@...or.com>, x86 <x86@...nel.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	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>
Subject: Re: [PATCH v2 03/44] x86/asm/head: rename 'stack_start' ->
 'initial_stack'

On Sat, Aug 06, 2016 at 07:25:21AM +0200, Borislav Petkov wrote:
> On Fri, Aug 05, 2016 at 11:01:57AM -0500, Josh Poimboeuf wrote:
> > The 8 should be changed to SIZEOF_PTREGS in a later patch
> > ("x86/asm/head: standardize the end of the stack for idle tasks").
> 
> But SIZEOF_PTREGS is 21*8. I don't understand.

I was referring to this patch:

  [PATCH v2 41/44] x86/asm/head: standardize the end of the stack for idle tasks
  https://lkml.kernel.org/r/98f297ffbc2a23131f08c5c77c4db974e0de2ad3.1470345772.git.jpoimboe@redhat.com

It changes the stack end offset from 8 to SIZEOF_PTREGS, so idle tasks
will have the same end of stack address that other tasks do.  I was
thinking we should make a similar change here, for consistency:

	/*
	 * Setup stack for verify_cpu(). "-8" because stack_start is defined
	 * this way, see below. Our best guess is a NULL ptr for stack
	 * termination heuristics and we don't want to break anything which
	 * might depend on it (kgdb, ...).
	 */
	leaq	(__end_init_task - 8)(%rip), %rsp

-- 
Josh