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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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.


>  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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