xen-netback: use jiffies_64 value to calculate credit timeout

time_after_eq() only works if the delta is < MAX_ULONG/2.

For a 32bit Dom0, if netfront sends packets at a very low rate, the time
between subsequent calls to tx_credit_exceeded() may exceed MAX_ULONG/2
and the test for timer_after_eq() will be incorrect. Credit will not be
replenished and the guest may become unable to send packets (e.g., if
prior to the long gap, all credit was exhausted).

Use jiffies_64 variant to mitigate this problem for 32bit Dom0.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Jason Luan <jianhai.luan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 7 insertions, 7 deletions

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index 5715318d6bab..400fea1de080 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -163,6 +163,7 @@ struct xenvif {
         unsigned long   credit_usec;
         unsigned long   remaining_credit;
         struct timer_list credit_timeout;
+        u64 credit_window_start;
 
         /* Statistics */
         unsigned long rx_gso_checksum_fixup;
diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index 01bb854c7f62..459935a6bfae 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -312,8 +312,7 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
         vif->credit_bytes = vif->remaining_credit = ~0UL;
         vif->credit_usec  = 0UL;
         init_timer(&vif->credit_timeout);
-        /* Initialize 'expires' now: it's used to track the credit window. */
-        vif->credit_timeout.expires = jiffies;
+        vif->credit_window_start = get_jiffies_64();
 
         dev->netdev_ops = &xenvif_netdev_ops;
         dev->hw_features = NETIF_F_SG | NETIF_F_IP_CSUM | NETIF_F_TSO;
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index f3e591c611de..900da4b243ad 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1185,9 +1185,8 @@ out:
 
 static bool tx_credit_exceeded(struct xenvif *vif, unsigned size)
 {
-        unsigned long now = jiffies;
-        unsigned long next_credit =
-                vif->credit_timeout.expires +
+        u64 now = get_jiffies_64();
+        u64 next_credit = vif->credit_window_start +
                 msecs_to_jiffies(vif->credit_usec / 1000);
 
         /* Timer could already be pending in rare cases. */
@@ -1195,8 +1194,8 @@ static bool tx_credit_exceeded(struct xenvif *vif, unsigned size)
                 return true;
 
         /* Passed the point where we can replenish credit? */
-        if (time_after_eq(now, next_credit)) {
-                vif->credit_timeout.expires = now;
+        if (time_after_eq64(now, next_credit)) {
+                vif->credit_window_start = now;
                 tx_add_credit(vif);
         }
 
@@ -1208,6 +1207,7 @@ static bool tx_credit_exceeded(struct xenvif *vif, unsigned size)
                         tx_credit_callback;
                 mod_timer(&vif->credit_timeout,
                           next_credit);
+                vif->credit_window_start = next_credit;
 
                 return true;
         }