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

[David Vrabel <david.vrabel@citrix.com>]

On 04/12/13 15:52, Ian Campbell wrote:
> 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.
                 ^forced
> 
> The potential for failure only exists for autotranslated guest (e.g. ARM and
> x86 PVH).
[...]
> --- 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);

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

David