[Xen-devel] [PATCH] xen: privcmd: do not return pages which we have failed to unmap

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

This failure represents a hypervisor issue, but if it does occur then nothing
good can come of returning pages which still refer to a foreign owned page
into the general allocation pool.

Instead we are foced to leak them. Log that we have done so.

The potential for failure only exists for autotranslated guest (e.g. ARM and
x86 PVH).

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
---
 drivers/xen/privcmd.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 8e74590..2efc720 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -533,11 +533,17 @@ static void privcmd_close(struct vm_area_struct *vma)
 {
        struct page **pages = vma->vm_private_data;
        int numpgs = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+       int rc;
 
        if (!xen_feature(XENFEAT_auto_translated_physmap) || !numpgs || !pages)
                return;
 
-       xen_unmap_domain_mfn_range(vma, numpgs, pages);
+       rc = xen_unmap_domain_mfn_range(vma, numpgs, pages);
+       if (rc < 0) {
+               pr_crit("unable to unmap MFN range: leaking %d pages\n",
+                       numpgs);
+               return;
+       }
        free_xenballooned_pages(numpgs, pages);
        kfree(pages);
 }
-- 
1.7.10.4


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