linux-kernel - Re: [PATCH v2 02/12] KVM: x86: tag the instructions which are used to write page table

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Message-ID: <4E39021F.8070508@redhat.com>
Date:	Wed, 03 Aug 2011 11:09:03 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 02/12] KVM: x86: tag the instructions which are used
 to write page table

On 08/03/2011 09:02 AM, Xiao Guangrong wrote:
> >  Note we don't need to actually emulate, just decode, since page_fault can tell us whether a write failed due to page tables or mmio.
> >
>
> This is a interesting feature. If it happens, i will just drop the shadow pages
> and retry these instructions directly.

Note it's a little dangerous.  If the guest uses a non-page-table 
modifying instruction on the PDE that points to the instruction, then we 
will unmap the instruction and go to an infinite loop.

Maybe it's better to emulate if we can't find a fix for that.

One way would be to emulate every 20 instructions; this breaks us out of 
the loop but reduces costly emulations to 5%.

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

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