linux-kernel - Re: Dealing with the NMI mess

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Message-ID: <20150724133343.GM18673@twins.programming.kicks-ass.net>
Date:	Fri, 24 Jul 2015 15:33:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Willy Tarreau <w@....eu>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: Dealing with the NMI mess

On Fri, Jul 24, 2015 at 03:30:13PM +0200, Peter Zijlstra wrote:
> > > But do we care if we do hit one? The return from the #DB handler can
> > > use a RET. Right?
> 
> Look at do_debug(), it has lovely bits like:
> 
> 	preempt_conditional_sti();
> 
> in it, we do _NOT_ want to be re-enabling interrupts if we're called
> from an !IF context, that'd be _bad_.

Ah, I forgot the conditional thing was the STI depending on regs->flags
& IF..

In any case, better safe than sorry and simply not do #DB ever if !IF.
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