linux-kernel - Re: mmiotrace bug: recursive probe hit

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Message-ID: <47F7A190.9070401@qumranet.com>
Date:	Sat, 05 Apr 2008 18:58:08 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
CC:	Pekka Paalanen <pq@....fi>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Christoph Hellwig <hch@...radead.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Pavel Roskin <proski@....org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	vegard.nossum@...il.com
Subject: Re: mmiotrace bug: recursive probe hit

Avi Kivity wrote:
>>
>> For kmemcheck, I'd prefer the per-CPU page tables suggested by Ingo.
>> I'm having hard time understanding why that's a "ugly hack" compared
>> to using kvm for this...
>>   
>
> It's not an ugly hack, but will be very very difficult.  With mmu 
> notifiers it's probably doable though:
>
> - the linux page tables are never loaded into cr3, but rather kept as 
> a reference
> - page faults are by instantiating ptes into shadow page tables (which 
> track the linux page tables)
> - mmu notifiers are used to drop shadow ptes when the linux ptes change
>

Actually, paravirt_ops is a much better match, as it also provides hooks 
for setting cr3.  I think you can implement per-cpu pagetables using 
paravirt_ops without modifying core mm code at all.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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