Commit ac3d5ac2 authored by Paul Durrant's avatar Paul Durrant Committed by David S. Miller
Browse files

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: default avatarPaul Durrant <>
Acked-by: default avatarWei Liu <>
Cc: Ian Campbell <>
Cc: David Vrabel <>
Signed-off-by: default avatarDavid S. Miller <>
parent 7a399e3a
......@@ -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.
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];
......@@ -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) *
if (vif->grant_copy_op == NULL) {
pr_warn("Could not allocate grant copy space for %s\n", name);
return ERR_PTR(-ENOMEM);
vif->domid = domid;
vif->handle = handle;
vif->can_sg = 1;
......@@ -487,6 +496,7 @@ void xenvif_free(struct xenvif *vif)
......@@ -608,7 +608,7 @@ void xenvif_rx_action(struct xenvif *vif)
if (!npo.copy_prod)
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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