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    Subject[PATCH 3.16.y-ckt 074/128] xen-netback: don't use last request to determine minimum Tx credit
    Date
    3.16.7-ckt23 -stable review patch.  If anyone has any objections, please let me know.

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

    From: David Vrabel <david.vrabel@citrix.com>

    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@citrix.com>
    Signed-off-by: David Vrabel <david.vrabel@citrix.com>
    Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Signed-off-by: Luis Henriques <luis.henriques@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 09e4f4ef4eb8..70e73907db0d 100644
    --- a/drivers/net/xen-netback/netback.c
    +++ b/drivers/net/xen-netback/netback.c
    @@ -755,9 +755,7 @@ static void tx_add_credit(struct xenvif_queue *queue)
    * 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(&queue->tx, queue->tx.req_cons)->size;
    - max_burst = min(max_burst, 131072UL);
    - max_burst = max(max_burst, queue->credit_bytes);
    + max_burst = max(131072UL, queue->credit_bytes);

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