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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Dec 06, 2013 at 05:58:25PM +0000, Stefano Stabellini wrote:
> On Wed, 4 Dec 2013, Ian Campbell wrote:
> > >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
> 
> 
> Acked-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> 
> Konrad, you can go ahead and add it to xentip, unless you would rather
> have me do it.

Why don't you do it. Thanks!
> 
> 
> >  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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