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Date: Tue, 3 Nov 2009 21:29:24 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Jan Kiszka <jan.kiszka@web.de>
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
       Prasad <prasad@linux.vnet.ibm.com>,
       Alan Stern <stern@rowland.harvard.edu>,
       Peter Zijlstra <peterz@infradead.org>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       Steven Rostedt <rostedt@goodmis.org>, Jiri Slaby <jirislaby@gmail.com>,
       Li Zefan <lizf@cn.fujitsu.com>, Avi Kivity <avi@redhat.com>,
       Paul Mackerras <paulus@samba.org>, Mike Galbraith <efault@gmx.de>,
       Masami Hiramatsu <mhiramat@redhat.com>,
       Paul Mundt <lethal@linux-sh.org>
Subject: Re: [PATCH 4/6] hw-breakpoints: Rewrite the hw-breakpoints layer
	on top of perf events
Message-ID: <20091103202923.GB4962@nowhere>
References: <1257275474-5285-1-git-send-email-fweisbec@gmail.com> <1257275474-5285-5-git-send-email-fweisbec@gmail.com> <4AF08B7C.8040903@web.de> <20091103201503.GA4962@nowhere> <4AF090EC.5010105@web.de>
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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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