linux-kernel - Re: Dealing with the NMI mess

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Message-ID: <20150724162550.GG3612@1wt.eu>
Date:	Fri, 24 Jul 2015 18:25:50 +0200
From:	Willy Tarreau <w@....eu>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>, 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 08:48:57AM -0700, Andy Lutomirski wrote:
> So by the time we detect that we've hit a watchpoint, the instruction
> that tripped it is done and we don't need RF.  Furthermore, after
> reading 17.3.1.1: I *think* that regs->flags withh have RF *clear* if
> we hit a watchpoint.

Apparently after reading 17.3.1.1, it seems like RF can still be set
if a data breakpoint triggers in a repeated string instruction before
the last iteration. However I don't think we care because as long as
we return to the string instruction, since the data location was already
visited it won't trigger again so the loss of the flag should be safe.

Willy

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