From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH v2 02/12] KVM: x86: tag the instructions which are used
 to write page table
Date: Wed, 03 Aug 2011 12:25:43 +0300
Message-ID: <4E391417.6050503@redhat.com>
References: <4E37DA49.1040000@cn.fujitsu.com> <4E37DA73.7010908@cn.fujitsu.com> <4E37EB8E.6080207@redhat.com> <4E38E477.2000208@cn.fujitsu.com> <4E39021F.8070508@redhat.com> <4E3913CC.7010907@cn.fujitsu.com>
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Cc: Marcelo Tosatti <mtosatti@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>, KVM <kvm@vger.kernel.org>
To: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
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On 08/03/2011 12:24 PM, Xiao Guangrong wrote:
> >  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%.
> >
>
> After much thought about this, may be this optimization is not good s=
ince:
> - it is little complex
> - this optimization is only applied to the instruction emulation caus=
ed by #PF
> - it does not improve too much:
>    if we emulate the instruction, we need to do:
>    - decode instruction
>    - emulate it
>    - zap shadow pages
>    And do this, it can return to the guest, the guest can run the nex=
t instruction
>
>    if we retry the instruction, we need to do:
>    - decode instruction
>    - zap shadow pages
>    then return to the guest and retry the instruction, however, we wi=
ll get page fault
>    again(since the mapping is still read-only), so we will get anothe=
r VM-exit and need
>    to do:
>    # trigger page fault
>    - handle the page fault and change the mapping to writable
>    - retry the instruction
>    until now, the guest can run the next instruction
>
> So, i do not think the new way is better, your opinion=EF=BC=9F

We can change to writeable and zap in the same exit, no?  Basically cal=
l=20
page_fault() again after zapping.

--=20
error compiling committee.c: too many arguments to function