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

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Message-ID: <20140128011841.GG10323@ZenIV.linux.org.uk>
Date:	Tue, 28 Jan 2014 01:18:41 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Anvin <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	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 Mon, Jan 27, 2014 at 06:39:31PM +0100, Oleg Nesterov wrote:
> On 01/27, Al Viro wrote:
> >
> > BTW, there's an additional pile of obfuscation:
> > /* work to do on interrupt/exception return */
> > #define _TIF_WORK_MASK                                                  \
> >         (0x0000FFFF &                                                   \
> >          ~(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|                       \
> >            _TIF_SINGLESTEP|_TIF_SECCOMP|_TIF_SYSCALL_EMU))
> >
> > /* work to do on any return to user space */
> > #define _TIF_ALLWORK_MASK                                               \
> >         ((0x0000FFFF & ~_TIF_SECCOMP) | _TIF_SYSCALL_TRACEPOINT |       \
> >         _TIF_NOHZ)
> 
> Heh, yes ;)
> 
> > Why is _TIF_UPROBE *not* a part
> > of _TIF_DO_NOTIFY_MASK, for example?
> 
> Yes, please see another email. That is why uprobe_deny_signal()
> sets TIF_NOTIFY_RESUME along with TIF_UPROBE.

*grumble* Can it end up modifying *regs?  From very cursory reading of
kernel/events/uprobe.c it seems to do so, so we probably want to leave
via iretq if that has hit, right?
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