linux-kernel - Re: [PATCH] xen/xenbus: Don't leak memory when unmapping the ring on HVM backend

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Date:	Mon, 10 Aug 2015 19:46:37 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	Julien Grall <julien.grall@...rix.com>
CC:	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>
Subject: Re: [PATCH] xen/xenbus: Don't leak memory when unmapping the ring on
 HVM backend

On Mon, Aug 10, 2015 at 07:10:38PM +0100, Julien Grall wrote:
> The commit ccc9d90a9a8b5c4ad7e9708ec41f75ff9e98d61d "xenbus_client:
> Extend interface to support multi-page ring" removes the call to
> free_xenballooned_pages in xenbus_unmap_ring_vfree_hvm.
> 
> This will result to not give back the pages to Linux and loose them
> forever. It only happens when the backends are running in HVM domains.
> 
> Signed-off-by: Julien Grall <julien.grall@...rix.com>
> 
> ---
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> Cc: Wei Liu <wei.liu2@...rix.com>
> 

Reviewed-by: Wei Liu <wei.liu2@...rix.com>

> Appeared in Linux 4.1. HVM backend, which is always the case on ARM, will
> leak every mapped ring (i.e ~12KB per domain with 1 disk and 1 vif).
> ---
>  drivers/xen/xenbus/xenbus_client.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c
> index 9ad3272..e303535 100644
> --- a/drivers/xen/xenbus/xenbus_client.c
> +++ b/drivers/xen/xenbus/xenbus_client.c
> @@ -814,8 +814,10 @@ static int xenbus_unmap_ring_vfree_hvm(struct xenbus_device *dev, void *vaddr)
>  
>  	rv = xenbus_unmap_ring(dev, node->handles, node->nr_handles,
>  			       addrs);
> -	if (!rv)
> +	if (!rv) {
>  		vunmap(vaddr);
> +		free_xenballooned_pages(node->nr_handles, node->hvm.pages);
> +	}
>  	else
>  		WARN(1, "Leaking %p, size %u page(s)\n", vaddr,
>  		     node->nr_handles);
> -- 
> 2.1.4
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