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

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Message-ID: <20100718152321.GA20355@redhat.com>
Date:	Sun, 18 Jul 2010 18:23:21 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Avi Kivity <avi@...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 Sun, Jul 18, 2010 at 06:14:11PM +0300, Avi Kivity wrote:
> 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
So do we or don't we want to COW on write faults?

--
			Gleb.
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