Re: [Xen-devel] Re: Next steps with pv_ops for Xen

[Derek Murray <Derek.Murray@xxxxxxxxxxxx>]

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.

# HG changeset patch
# User dgm36@xxxxxxxxxxxxxxxx
# 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@xxxxxxxxxxxx>

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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