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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 6 Dec 2013, Konrad Rzeszutek Wilk wrote:
> 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!

done


> > 
> > >  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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