linux-kernel - Re: Dealing with the NMI mess

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Message-ID: <20150724111621.34713023@gandalf.local.home>
Date:	Fri, 24 Jul 2015 11:16:21 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Willy Tarreau <w@....eu>
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, 24 Jul 2015 16:59:01 +0200
Willy Tarreau <w@....eu> wrote:

> On Fri, Jul 24, 2015 at 10:31:27AM -0400, Steven Rostedt wrote:
> > On Fri, 24 Jul 2015 15:21:28 +0200
> > Willy Tarreau <w@....eu> wrote:
> > 
> > > My understanding is that by using RET we can't set the RF flag and #DB
> > 
> > But the RF flag is only set for instruction (executing) breakpoints. It
> > is not set for data (RW) ones.
> 
> True but these also are the most complicated to deal with. The data
> accesses can always be emulated (not what I'm suggesting here) while
> instructions are much harder to emulate.

The point is, if we trigger a #DB on an instruction breakpoint
while !IF, then we simply disable that breakpoint and do the RET. What
emulation is needed?

-- Steve
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