linux-kernel - Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)

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Message-ID: <4B5455FF.7010409@redhat.com>
Date:	Mon, 18 Jan 2010 14:37:19 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	ananth@...ibm.com, Jim Keniston <jkenisto@...ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	utrace-devel <utrace-devel@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Maneesh Soni <maneesh@...ibm.com>,
	Mark Wielaard <mjw@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)

On 01/18/2010 02:14 PM, Peter Zijlstra wrote:
>
>> Well, the alternatives are very unappealing.  Emulation and
>> single-stepping are going to be very slow compared to a couple of jumps.
>>      
> With CPL2 or RPL on user segments the protection issue seems to be
> manageable for running the instructions from kernel space.
>    

CPL2 gives unrestricted access to the kernel address space; and RPL does 
not affect page level protection.  Segment limits don't work on x86-64.  
But perhaps I missed something - these things are tricky.

It should be possible to translate the instruction into an address space 
check, followed by the action, but that's still slower due to privilege 
level switches.

-- 
error compiling committee.c: too many arguments to function

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