linux-kernel - Re: Dealing with the NMI mess

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Date:	Fri, 24 Jul 2015 17:49:26 +0200
From:	Willy Tarreau <w@....eu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <peterz@...radead.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 11:34:26AM -0400, Steven Rostedt wrote:
> On Fri, 24 Jul 2015 17:26:37 +0200
> Willy Tarreau <w@....eu> wrote:
> 
>  
> > > The point is, if we trigger a #DB on an instruction breakpoint
> > > while !IF, then we simply disable that breakpoint and do the RET.
> > 
> > Yes but the breakpoint remains disabled then. Or I'm missing
> > something.
> 
> Do we care? If it was an instruction breakpoint with !IF set, then it
> had to have happened in the kernel. And kgdb or whatever added it there
> needs to deal with that.

I was concerned that an RW BP would remain disabled when returning to
user space but Peter cleared that out by pointing me to the discussion
where it was explained that they are re-enabled when returning to user
space.

So no problem here for me.

Thanks,
Willy

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