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authorJan Beulich <JBeulich@suse.com>2016-05-04 07:02:36 -0600
committerDavid Vrabel <david.vrabel@citrix.com>2016-05-04 16:37:01 +0100
commit27e0e6385377c4dc68a4ddaf1a35a2dfa951f3c5 (patch)
tree940f070cecbb3f335be0c1f976a472c990ebf4ab
parentdfd74a1edfaba5864276a2859190a8d242d18952 (diff)
xen/evtchn: fix ring resize when binding new events
The copying of ring data was wrong for two cases: For a full ring nothing got copied at all (as in that case the canonicalized producer and consumer indexes are identical). And in case one or both of the canonicalized (after the resize) indexes would point into the second half of the buffer, the copied data ended up in the wrong (free) part of the new buffer. In both cases uninitialized data would get passed back to the caller. Fix this by simply copying the old ring contents twice: Once to the low half of the new buffer, and a second time to the high half. This addresses the inability to boot a HVM guest with 64 or more vCPUs. This regression was caused by 8620015499101090 (xen/evtchn: dynamically grow pending event channel ring). Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Signed-off-by: Jan Beulich <jbeulich@suse.com> Cc: <stable@vger.kernel.org> # 4.4+ Signed-off-by: David Vrabel <david.vrabel@citrix.com>
-rw-r--r--drivers/xen/evtchn.c20
1 files changed, 8 insertions, 12 deletions
diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
index 38272ad24551..f4edd6df3df2 100644
--- a/drivers/xen/evtchn.c
+++ b/drivers/xen/evtchn.c
@@ -316,7 +316,6 @@ static int evtchn_resize_ring(struct per_user_data *u)
{
unsigned int new_size;
evtchn_port_t *new_ring, *old_ring;
- unsigned int p, c;
/*
* Ensure the ring is large enough to capture all possible
@@ -346,20 +345,17 @@ static int evtchn_resize_ring(struct per_user_data *u)
/*
* Copy the old ring contents to the new ring.
*
- * If the ring contents crosses the end of the current ring,
- * it needs to be copied in two chunks.
+ * To take care of wrapping, a full ring, and the new index
+ * pointing into the second half, simply copy the old contents
+ * twice.
*
* +---------+ +------------------+
- * |34567 12| -> | 1234567 |
- * +-----p-c-+ +------------------+
+ * |34567 12| -> |34567 1234567 12|
+ * +-----p-c-+ +-------c------p---+
*/
- p = evtchn_ring_offset(u, u->ring_prod);
- c = evtchn_ring_offset(u, u->ring_cons);
- if (p < c) {
- memcpy(new_ring + c, u->ring + c, (u->ring_size - c) * sizeof(*u->ring));
- memcpy(new_ring + u->ring_size, u->ring, p * sizeof(*u->ring));
- } else
- memcpy(new_ring + c, u->ring + c, (p - c) * sizeof(*u->ring));
+ memcpy(new_ring, old_ring, u->ring_size * sizeof(*u->ring));
+ memcpy(new_ring + u->ring_size, old_ring,
+ u->ring_size * sizeof(*u->ring));
u->ring = new_ring;
u->ring_size = new_size;