linux-kernel - Re: [PATCH 5/6] kvm, x86: use ro page and don't copy shared page

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Message-ID: <4C431A43.5010808@redhat.com>
Date:	Sun, 18 Jul 2010 18:14:11 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 5/6] kvm, x86: use ro page and don't copy shared page

On 07/17/2010 07:31 AM, Gleb Natapov wrote:
>>>
>>> Currently pages allocated for guest memory are required to be RW, so after your series
>>> behaviour will remain exactly the same as before.
>>>        
>> Except KSM pages.
>>
>>      
> KSM page will be COWed by __get_user_pages_fast(addr, 1, 1, page) in
> get_user_page_and_protection() just like it COWed now, no?
>    

Well, we don't want to COW it on write faults.

The optimal behaviour is:

- write faults: COW and instantiate a writeable spte
- read faults: instantiate a readable spte; if likely(page is 
writeable), make it a writeable spte; if likely(page is dirty) make it a 
dirty spte
- speculative spte instantiations: if likely(page is present) 
instantiate a pte; if accessed, mark it accessed, if writeable, mark it 
writeable; if dirty, mark it dirty

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

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