[3.13.y-ckt stable] Patch "xen-netback: don't use last request to determine minimum Tx credit" has been added to the 3.13.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt33.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From a5bf64933bd4d4b514feed31aeae34f010d706a9 Mon Sep 17 00:00:00 2001
From: David Vrabel <david.vrabel at citrix.com>
Date: Fri, 30 Oct 2015 15:16:01 +0000
Subject: 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.

Reviewed-by: Wei Liu <wei.liu2 at citrix.com>
Signed-off-by: David Vrabel <david.vrabel at citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
[ kamal: backport to 3.13-stable: context ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/net/xen-netback/netback.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index b898c6b..7d76d28 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -716,9 +716,7 @@ 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;
--
1.9.1