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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

> > -   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);
> 
> kfree(pages) here?  I think that would be safe. Although at this point
> it probably doesn't really matter.

I suppose we might as well not make it any worse than it needs to be and
it's easy enough to arrange.

---------------------8<---------------------

From 900f1e903bacf376800b078aef03e8d5ff524562 Mon Sep 17 00:00:00 2001
From: Ian Campbell <ian.campbell@xxxxxxxxxx>
Date: Wed, 4 Dec 2013 14:19:52 +0000
Subject: [PATCH] xen: privcmd: do not return pages which we have failed to
 unmap

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 forced 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
---
v2: Don't leak the actual pages array as well
    Log rc
---
 drivers/xen/privcmd.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 8e74590..569a13b 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -533,12 +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);
-       free_xenballooned_pages(numpgs, pages);
+       rc = xen_unmap_domain_mfn_range(vma, numpgs, pages);
+       if (rc == 0)
+               free_xenballooned_pages(numpgs, pages);
+       else
+               pr_crit("unable to unmap MFN range: leaking %d pages. rc=%d\n",
+                       numpgs, rc);
        kfree(pages);
 }
 
-- 
1.7.10.4




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