linux-kernel - Re: [PATCH 2/5] x86/entry/64, entry: Set up a valid sysenter stack and prepare for 32-bit merge

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Message-ID: <20150723120125.7c6d74d3@gandalf.local.home>
Date:	Thu, 23 Jul 2015 12:01:25 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	X86 ML <x86@...nel.org>, linux-kernel@...r.kernel.org,
	Willy Tarreau <w@....eu>, Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 2/5] x86/entry/64, entry: Set up a valid sysenter stack
 and prepare for 32-bit merge

On Thu, 23 Jul 2015 08:31:40 -0700
Andy Lutomirski <luto@...nel.org> wrote:

> Oddly, 64-bit kernels already allocate a percpu sysenter stack, but
> they don't enable it.  Enable the stack and tweak the rest of the
> sysenter setup code to be similar to the 32-bit version.

I'm curious. Did you do any investigation into the 64bit code to why it
wasn't set? Do you know if that was just overlooked with some of the
merging between i386 and x86_64 systems?

I'm not asking you to do it if you have not, but if you have, I think
it would be more comforting to know that it was just overlooked than
there being some other subtle reason.

-- Steve

> 
> This eliminates the only place in the kernel in which TF could be set
> without a valid stack.
> 
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