xen-netback: don't use last request to determine minimum Tx credit

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.

CC: stable@vger.kernel.org
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
[bwh: Backported to 3.2: s/queue/vif/g]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index b2528f6..0c0b768 100644 (file)
--- 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 *vif)
         * 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;