From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [PATCH 1/3] kvm: dont hold pagecount reference for mapped
	sptes pages.
Date: Thu, 9 Apr 2009 06:54:08 -0300
Message-ID: <20090409095408.GA31724@amt.cnet>
References: <1238457604-7637-1-git-send-email-ieidus@redhat.com> <1238457604-7637-2-git-send-email-ieidus@redhat.com>
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To: Izik Eidus <ieidus@redhat.com>
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On Tue, Mar 31, 2009 at 03:00:02AM +0300, Izik Eidus wrote:
> When using mmu notifiers, we are allowed to remove the page count
> reference tooken by get_user_pages to a specific page that is mapped
> inside the shadow page tables.
> 
> This is needed so we can balance the pagecount against mapcount
> checking.
> 
> (Right now kvm increase the pagecount and does not increase the
> mapcount when mapping page into shadow page table entry,
> so when comparing pagecount against mapcount, you have no
> reliable result.)

IMO ifdef'ing CONFIG_MMU_NOTIFIERS here (and keeping the ref if unset)
instead of in the backward compat code gives less room for headaches.