Re: Re: Next steps with pv_ops for Xen

[Derek Murray <Derek.Murray@cl.cam.ac.uk>]

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Keir Fraser wrote:
> Is this patch to go into linux-2.6.18-xen.hg then?

Yes, even if it doesn't fix the exact bug we're seeing here, I think it 
should go in. I've attached a version with my signed-off-by and a better 
commit comment.

Cheers,

Derek.

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# HG changeset patch
# User dgm36@ise.cl.cam.ac.uk
# Date 1196860382 0
# Node ID af26b3dd23822190acbec1872a47259e1fed88b8
# Parent  b2768401db943e66af9d64bd610ffa225f560c0b
Add VM_PFNMAP flag to gntdev-mmaped VM areas. This prevents an attempt in
zap_pte_range to decrement the reverse-mapping count of the non-existant
(but occasionally spuriously present) page_struct associated with the
granted PFN.

Signed-off-by: Derek Murray <Derek.Murray@cl.cam.ac.uk>

diff -r b2768401db94 -r af26b3dd2382 drivers/xen/gntdev/gntdev.c
--- a/drivers/xen/gntdev/gntdev.c	Mon Dec 03 08:50:12 2007 +0000
+++ b/drivers/xen/gntdev/gntdev.c	Wed Dec 05 13:13:02 2007 +0000
@@ -501,6 +501,17 @@ static int gntdev_mmap (struct file *fli
     
 	/* The VM area contains pages from another VM. */
 	vma->vm_flags |= VM_FOREIGN;
+
+	/* The VM area contains pages that are not backed by page_structs in
+	 * this domain's memory map.
+	 *
+	 * TODO/FIXME?: We should probably use the VM_FOREIGN workaround as
+	 *              used by get_user_pages() to provide access to the
+	 *              page_structs for each page, but I'm not sure if that's
+	 *              necessary.
+	 */
+	vma->vm_flags |= VM_PFNMAP;
+
 	vma->vm_private_data = kzalloc(size * sizeof(struct page_struct *), 
 				       GFP_KERNEL);
 	if (vma->vm_private_data == NULL) {

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