From mboxrd@z Thu Jan  1 00:00:00 1970
From: George Dunlap <george.dunlap@eu.citrix.com>
Subject: Re: xenheap pages mapped by dom0
Date: Fri, 18 Dec 2009 15:29:15 +0000
Message-ID: <4B2B9FCB.6010309@eu.citrix.com>
References: <C7514F4A.4C35%keir.fraser@eu.citrix.com>
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To: Keir Fraser <Keir.Fraser@eu.citrix.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, Jan Beulich <JBeulich@novell.com>
List-Id: xen-devel@lists.xenproject.org

Keir Fraser wrote:
> I think the right thing to do would be very roughly:
> On allocation:
>  page = alloc_xenheap_page();
>  share_xen_page_with_guest(page);
> On deallocation:
>  if (test_and_clear(PGC_allocated)) put_page();
>  if (page->count_info & PGC_count_mask) return -EBUSY;
>  free_xenheap_page(page);
>   
Hmm, the first two should probably happen in the opposite order, no?  
I.e., we should check to see that for each page we want to deallocate, 
page->count_info & PGC_count_mask == 0, returning -EBUSY if that fails; 
then unmark allocate and call free xenheap page?

 -George