From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: [PATCH 11/12] xen/gntdev: mark userspace PTEs as
 special on x86 PV guests
Date: Wed, 7 Jan 2015 12:11:14 +0000
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To: David Vrabel <david.vrabel@citrix.com>
Cc: xen-devel@lists.xenproject.org, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Jenny Herbert <jennifer.herbert@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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On Tue, 2015-01-06 at 18:57 +0000, David Vrabel wrote:
> In an x86 PV guest, get_user_pages_fast() on a userspace address range
> containing foreign mappings does not work correctly because the M2P
> lookup of the MFN from a userspace PTE may return the wrong page.
> 
> Force get_user_pages_fast() to fail on such addresses by marking the PTEs
> as special.
> 
> If Xen has XENFEAT_gnttab_map_avail_bits (available since at least
> 4.0),

http://wiki.xenproject.org/wiki/Xen_Kernel_Feature_Matrix says the dom0
pvpops already requires >= 4.0 too, which matches my recollection
(something to do with a new APIC interface which upstream insisted on
during upstreaming, IIRC), but both could be out of date...

Ian.