From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753212AbbCWR2N (ORCPT <rfc822;w@1wt.eu>);
	Mon, 23 Mar 2015 13:28:13 -0400
Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.231]:35015 "EHLO
	cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL)
	by vger.kernel.org with ESMTP id S1752285AbbCWR2K (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 23 Mar 2015 13:28:10 -0400
Date: Mon, 23 Mar 2015 13:28:47 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] x86: stop using PER_CPU_VAR(kernel_stack)
Message-ID: <20150323132847.79e18ea5@grimm.local.home>
In-Reply-To: <551048E9.6060800@redhat.com>
References: <1426970678-600-1-git-send-email-dvlasenk@redhat.com>
	<20150323101815.35bd61c7@gandalf.local.home>
	<551048E9.6060800@redhat.com>
X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
X-RR-Connecting-IP: 107.14.168.118:25
X-Cloudmark-Score: 0
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, 23 Mar 2015 18:10:01 +0100
Denys Vlasenko <dvlasenk@redhat.com> wrote:

> On 03/23/2015 03:18 PM, Steven Rostedt wrote:
> > On Sat, 21 Mar 2015 21:44:37 +0100
> > Denys Vlasenko <dvlasenk@redhat.com> wrote:
> > 
> >> Instead of PER_CPU_VAR(kernel_stack), 64-bit code
> >> can use PER_CPU_VAR(cpu_tss + TSS_sp0).
> > 
> > The change log here is lacking an answer to "why". It only states what
> > it does. What's wrong with using kernel_stack? The change log should
> > explicitly state that. I have no idea why this patch is needed.
> 
> Sorry. The reason is:
> 
> We want to get rid of kernel_stack, since it is redundant:
> in 64-bits, PER_CPU_VAR(cpu_tss + TSS_sp0) can be used instead,
> in 32-bits, PER_CPU_VAR(cpu_current_top_of_stack) can be used instead.

Can we do a:

 #define cpu_current_top_of_stack (cpu_tss + TSS_sp0)

in 64-bit, and make it consistent with i386.

"cpu_tss + TSS_sp0" is rather meaningless. "kernel_stack" or
"top_of_stack" is at least informative.

> 
> Patch 2/2 in the same series removes kernel_stack.

Understood, but each commit's change log should be able to stand on its
own.

-- Steve