linux-kernel - Re: [PATCH v2 05/12] KVM: x86: fast emulate repeat string write instructions

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Message-ID: <4E39155A.6090704@cn.fujitsu.com>
Date:	Wed, 03 Aug 2011 17:31:06 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 05/12] KVM: x86: fast emulate repeat string write instructions

On 08/03/2011 04:10 PM, Avi Kivity wrote:
> On 08/02/2011 02:09 PM, Xiao Guangrong wrote:
>> We usually use repeat string instructions to clear the page, for example,
>> we call memset to clear a page table, stosb is used in this function, and
>> repeated for 1024 times, that means we should occupy mmu lock for 1024 times
>> and walking shadow page cache for 1024 times, it is terrible
>>
>> In fact, if it is the repeat string instructions emulated and it is not a
>> IO/MMIO access, we can zap all the corresponding shadow pages and return to the
>> guest, then the mapping can became writable and we can directly write the page
>>
> 
> This isn't needed if we zap before emulating, right?
> 

Yes, it is, i will improve it.
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