Re: [PATCH 1/3] kvm: dont hold pagecount reference for mapped sptes pages.

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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.

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