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

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Date:	Mon, 10 Aug 2015 19:10:38 +0100
From:	Julien Grall <julien.grall@...rix.com>
To:	<xen-devel@...ts.xenproject.org>
CC:	<linux-kernel@...r.kernel.org>,
	Julien Grall <julien.grall@...rix.com>,
	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: [PATCH] xen/xenbus: Don't leak memory when unmapping the ring on HVM backend

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>

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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