linux-kernel - Re: [RFC] de-asmify the x86-64 system call slowpath

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Message-ID: <CA+55aFzCtJ5gfw__3A=zkjJdv9Ag2CAmtHG5MnrRnCZYqz7EQA@mail.gmail.com>
Date:	Sun, 26 Jan 2014 20:32:09 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Peter Anvin <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] de-asmify the x86-64 system call slowpath

On Sun, Jan 26, 2014 at 4:22 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> Umm...  Can't uprobe_notify_resume() modify regs as well?

Probably.

.. and on the other hand, we should actually be able to use 'sysret'
for signal handling on x86-64, because while sysret destroys %rcx and
doesn't allow for returning to odd modes, for calling a signal handler
I don't think we really care..

> While we
> are at it, when we start using the same thing on 32bit kernels, we'll
> need to watch out for execve() - the reason why start_thread() sets
> TIF_NOTIFY_RESUME is to force us away from sysexit path.  IIRC, vm86
> is another thing to watch out for (same reasons).

Yes, the 32-bit code I didn't want to touch, partly because I no
longer have a test-case. And it does end up having some more
interesting cases.

                 Linus
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