linux-kernel - Re: [PATCH 4/6] hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf events

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Date:	Mon, 26 Oct 2009 09:17:31 +0100
From:	Jan Kiszka <jan.kiszka@....de>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Prasad <prasad@...ux.vnet.ibm.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jiri Slaby <jirislaby@...il.com>,
	Li Zefan <lizf@...fujitsu.com>, Avi Kivity <avi@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Mike Galbraith <efault@....de>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Paul Mundt <lethal@...ux-sh.org>
Subject: Re: [PATCH 4/6] hw-breakpoints: Rewrite the hw-breakpoints layer
 on 	top of perf events

Frederic Weisbecker wrote:
> 2009/10/24 Jan Kiszka <jan.kiszka@....de>:
>> Since commit 3d53c27d05, KVM uses current->thread.debugregs for
>> restoring the host state in case the guest played with breakpoints. We
>> need an equivalent interface to restore ptrace breakpoints and all
>> others currently in use.
>>
>> Jan
> 
> 
> Well, dr6 is still stored in the current thread.
> dr7 has a per cpu variable containing its value.
> 
> So what remains is to have a per cpu variable for dr0-3
> which is updated when perf schedules in/out a profiled context.
> I can do that in a v3.

Sounds great. Maybe you can stuff all this into some function kvm can
call to avoid that it has to peek into various internal structures.

Jan


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