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Subject[PATCH 3.2 21/70] xen-netback: don't use last request to determine minimum Tx credit
3.2.76-rc1 review patch.  If anyone has any objections, please let me know.


From: David Vrabel <>

commit 0f589967a73f1f30ab4ac4dd9ce0bb399b4d6357 upstream.

The last from guest transmitted request gives no indication about the
minimum amount of credit that the guest might need to send a packet
since the last packet might have been a small one.

Instead allow for the worst case 128 KiB packet.

This is part of XSA155.

Reviewed-by: Wei Liu <>
Signed-off-by: David Vrabel <>
Signed-off-by: Konrad Rzeszutek Wilk <>
[bwh: Backported to 3.2: s/queue/vif/g]
Signed-off-by: Ben Hutchings <>
drivers/net/xen-netback/netback.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -864,9 +864,7 @@ static void tx_add_credit(struct xenvif
* Allow a burst big enough to transmit a jumbo packet of up to 128kB.
* Otherwise the interface can seize up due to insufficient credit.
- max_burst = RING_GET_REQUEST(&vif->tx, vif->tx.req_cons)->size;
- max_burst = min(max_burst, 131072UL);
- max_burst = max(max_burst, vif->credit_bytes);
+ max_burst = max(131072UL, vif->credit_bytes);

/* Take care that adding a new chunk of credit doesn't wrap to zero. */
max_credit = vif->remaining_credit + vif->credit_bytes;

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