From ac3d5ac277352fe6e27809286768e9f1f8aa388d Mon Sep 17 00:00:00 2001
From: Paul Durrant <Paul.Durrant@citrix.com>
Date: Mon, 23 Dec 2013 09:27:17 +0000
Subject: [PATCH] xen-netback: fix guest-receive-side array sizes
The sizes chosen for the metadata and grant_copy_op arrays on the guest
receive size are wrong;
- The meta array is needlessly twice the ring size, when we only ever
consume a single array element per RX ring slot
- The grant_copy_op array is way too small. It's sized based on a bogus
assumption: that at most two copy ops will be used per ring slot. This
may have been true at some point in the past but it's clear from looking
at start_new_rx_buffer() that a new ring slot is only consumed if a frag
would overflow the current slot (plus some other conditions) so the actual
limit is MAX_SKB_FRAGS grant_copy_ops per ring slot.
This patch fixes those two sizing issues and, because grant_copy_ops grows
so much, it pulls it out into a separate chunk of vmalloc()ed memory.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
drivers/net/xen-netback/common.h | 19 +++++++++++++------
drivers/net/xen-netback/interface.c | 10 ++++++++++
drivers/net/xen-netback/netback.c | 2 +-
3 files changed, 24 insertions(+), 7 deletions(-)
diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index 08ae01b41c832..c47794b9d42f9 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -101,6 +101,13 @@ struct xenvif_rx_meta {
#define MAX_PENDING_REQS 256
+/* It's possible for an skb to have a maximal number of frags
+ * but still be less than MAX_BUFFER_OFFSET in size. Thus the
+ * worst-case number of copy operations is MAX_SKB_FRAGS per
+ * ring slot.
+ */
+#define MAX_GRANT_COPY_OPS (MAX_SKB_FRAGS * XEN_NETIF_RX_RING_SIZE)
+
struct xenvif {
/* Unique identifier for this interface. */
domid_t domid;
@@ -143,13 +150,13 @@ struct xenvif {
*/
RING_IDX rx_req_cons_peek;
- /* Given MAX_BUFFER_OFFSET of 4096 the worst case is that each
- * head/fragment page uses 2 copy operations because it
- * straddles two buffers in the frontend.
- */
- struct gnttab_copy grant_copy_op[2*XEN_NETIF_RX_RING_SIZE];
- struct xenvif_rx_meta meta[2*XEN_NETIF_RX_RING_SIZE];
+ /* This array is allocated seperately as it is large */
+ struct gnttab_copy *grant_copy_op;
+ /* We create one meta structure per ring request we consume, so
+ * the maximum number is the same as the ring size.
+ */
+ struct xenvif_rx_meta meta[XEN_NETIF_RX_RING_SIZE];
u8 fe_dev_addr[6];
diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index 870f1fa583702..34ca4e58a43df 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -307,6 +307,15 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
SET_NETDEV_DEV(dev, parent);
vif = netdev_priv(dev);
+
+ vif->grant_copy_op = vmalloc(sizeof(struct gnttab_copy) *
+ MAX_GRANT_COPY_OPS);
+ if (vif->grant_copy_op == NULL) {
+ pr_warn("Could not allocate grant copy space for %s\n", name);
+ free_netdev(dev);
+ return ERR_PTR(-ENOMEM);
+ }
+
vif->domid = domid;
vif->handle = handle;
vif->can_sg = 1;
@@ -487,6 +496,7 @@ void xenvif_free(struct xenvif *vif)
unregister_netdev(vif->dev);
+ vfree(vif->grant_copy_op);
free_netdev(vif->dev);
module_put(THIS_MODULE);
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 7b4fd93be76dd..78425554a5375 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -608,7 +608,7 @@ void xenvif_rx_action(struct xenvif *vif)
if (!npo.copy_prod)
return;
- BUG_ON(npo.copy_prod > ARRAY_SIZE(vif->grant_copy_op));
+ BUG_ON(npo.copy_prod > MAX_GRANT_COPY_OPS);
gnttab_batch_copy(vif->grant_copy_op, npo.copy_prod);
while ((skb = __skb_dequeue(&rxq)) != NULL) {
--
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