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

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Message-ID: <20091103202923.GB4962@nowhere>
Date:	Tue, 3 Nov 2009 21:29:24 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jan Kiszka <jan.kiszka@....de>
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

On Tue, Nov 03, 2009 at 09:22:04PM +0100, Jan Kiszka wrote:
> > Thinking about it, this check should cover every cases:
> > 
> > if (vcpu->arch.switch_db_regs || __get_cpu_var(dr7) & DR_GLOBAL_ENABLE_MASK)
> > 
> > If we have __get_cpu_var(dr7) & DR_GLOBAL_ENABLE_MASK, it means there is an
> > active breakpoint and then we should restore the current state.
> > 
> 
> And what about (__get_cpu_var(dr7) & DR_GLOBAL_ENABLE_MASK) only? Would
> you be able to live with unsync'ed hardware and software states?
> 
> Jan
> 


But if the guest has breakpoints activated, the host will inherit
them, which is really not something we want, assuming vcpu->arch.switch_db_regs
already protects us about that.

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