linux-kernel - Re: Dealing with the NMI mess

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Message-ID: <20150724090342.6d11e16d@gandalf.local.home>
Date:	Fri, 24 Jul 2015 09:03:42 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	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>,
	Willy Tarreau <w@....eu>, 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 14:43:04 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

 
> > I'm not too familiar with how to use hw breakpoints, but I'm guessing
> > (correct me if I'm wrong) that breakpoints on code that trigger when
> > executed, but watchpoints on data trigger when accessed. Then
> > copy_from_user_inatomic() would only trigger on watchpoints (it's not
> > executing that code, at least I hope it isn't!), and those wont bother
> > us.
> 
> These things can be: RW, W, X.
> 
> Sure, hitting a user X watchpoint is going to be 'interesting', but its
> fairly easy to hit a RW one.

But do we care if we do hit one? The return from the #DB handler can
use a RET. Right?

-- Steve


> 
> Just watch an on-stack variable and get perf to copy a huge chunk of
> stack (like it does for the dwarf stuff).

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