e1000e: DoS while TSO enabled caused by link partner with small MSS

With a low enough MSS on the link partner and TSO enabled locally, the
networking stack can periodically send a very large (e.g.  64KB) TCP
message for which the driver will attempt to use more Tx descriptors than
are available by default in the Tx ring.  This is due to a workaround in
the code that imposes a limit of only 4 MSS-sized segments per descriptor
which appears to be a carry-over from the older e1000 driver and may be
applicable only to some older PCI or PCIx parts which are not supported in
e1000e.  When the driver gets a message that is too large to fit across the
configured number of Tx descriptors, it stops the upper stack from queueing
any more and gets stuck in this state.  After a timeout, the upper stack
assumes the adapter is hung and calls the driver to reset it.

Remove the unnecessary limitation of using up to only 4 MSS-sized segments
per Tx descriptor, and put in a hard failure test to catch when attempting
to check for message sizes larger than would fit in the whole Tx ring.
Refactor the remaining logic that limits the size of data per Tx descriptor
from a seemingly arbitrary 8KB to a limit based on the dynamic size of the
Tx packet buffer as described in the hardware specification.

Also, fix the logic in the check for space in the Tx ring for the next
largest possible packet after the current one has been successfully queued
for transmit, and use the appropriate defines for default ring sizes in
e1000_probe instead of magic values.

This issue goes back to the introduction of e1000e in 2.6.24 when it was
split off from e1000.
Reported-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Cc: Stable <stable@vger.kernel.org> [2.6.24+]
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/intel/e1000e/e1000.h

@@ -310,6 +310,7 @@ struct e1000_adapter {
 	 */
 	struct e1000_ring *tx_ring /* One per active queue */
 						____cacheline_aligned_in_smp;
+	u32 tx_fifo_limit;
 
 	struct napi_struct napi;
 

drivers/net/ethernet/intel/e1000e/netdev.c

@@ -3516,6 +3516,15 @@ void e1000e_reset(struct e1000_adapter *adapter)
 		break;
 	}
 
+	/*
+	 * Alignment of Tx data is on an arbitrary byte boundary with the
+	 * maximum size per Tx descriptor limited only to the transmit
+	 * allocation of the packet buffer minus 96 bytes with an upper
+	 * limit of 24KB due to receive synchronization limitations.
+	 */
+	adapter->tx_fifo_limit = min_t(u32, ((er32(PBA) >> 16) << 10) - 96,
+				       24 << 10);
+
 	/*
 	 * Disable Adaptive Interrupt Moderation if 2 full packets cannot
 	 * fit in receive buffer.
@@ -4785,12 +4794,9 @@ static bool e1000_tx_csum(struct e1000_ring *tx_ring, struct sk_buff *skb)
 	return 1;
 }
 
-#define E1000_MAX_PER_TXD	8192
-#define E1000_MAX_TXD_PWR	12
-
 static int e1000_tx_map(struct e1000_ring *tx_ring, struct sk_buff *skb,
 			unsigned int first, unsigned int max_per_txd,
-			unsigned int nr_frags, unsigned int mss)
+			unsigned int nr_frags)
 {
 	struct e1000_adapter *adapter = tx_ring->adapter;
 	struct pci_dev *pdev = adapter->pdev;
@@ -5023,20 +5029,19 @@ static int __e1000_maybe_stop_tx(struct e1000_ring *tx_ring, int size)
 
 static int e1000_maybe_stop_tx(struct e1000_ring *tx_ring, int size)
 {
+	BUG_ON(size > tx_ring->count);
+
 	if (e1000_desc_unused(tx_ring) >= size)
 		return 0;
 	return __e1000_maybe_stop_tx(tx_ring, size);
 }
 
-#define TXD_USE_COUNT(S, X) (((S) >> (X)) + 1)
 static netdev_tx_t e1000_xmit_frame(struct sk_buff *skb,
 				    struct net_device *netdev)
 {
 	struct e1000_adapter *adapter = netdev_priv(netdev);
 	struct e1000_ring *tx_ring = adapter->tx_ring;
 	unsigned int first;
-	unsigned int max_per_txd = E1000_MAX_PER_TXD;
-	unsigned int max_txd_pwr = E1000_MAX_TXD_PWR;
 	unsigned int tx_flags = 0;
 	unsigned int len = skb_headlen(skb);
 	unsigned int nr_frags;
@@ -5056,18 +5061,8 @@ static netdev_tx_t e1000_xmit_frame(struct sk_buff *skb,
 	}
 
 	mss = skb_shinfo(skb)->gso_size;
-	/*
-	 * The controller does a simple calculation to
-	 * make sure there is enough room in the FIFO before
-	 * initiating the DMA for each buffer.  The calc is:
-	 * 4 = ceil(buffer len/mss).  To make sure we don't
-	 * overrun the FIFO, adjust the max buffer len if mss
-	 * drops.
-	 */
 	if (mss) {
 		u8 hdr_len;
-		max_per_txd = min(mss << 2, max_per_txd);
-		max_txd_pwr = fls(max_per_txd) - 1;
 
 		/*
 		 * TSO Workaround for 82571/2/3 Controllers -- if skb->data
@@ -5097,12 +5092,12 @@ static netdev_tx_t e1000_xmit_frame(struct sk_buff *skb,
 		count++;
 	count++;
 
-	count += TXD_USE_COUNT(len, max_txd_pwr);
+	count += DIV_ROUND_UP(len, adapter->tx_fifo_limit);
 
 	nr_frags = skb_shinfo(skb)->nr_frags;
 	for (f = 0; f < nr_frags; f++)
-		count += TXD_USE_COUNT(skb_frag_size(&skb_shinfo(skb)->frags[f]),
-				       max_txd_pwr);
+		count += DIV_ROUND_UP(skb_frag_size(&skb_shinfo(skb)->frags[f]),
+				      adapter->tx_fifo_limit);
 
 	if (adapter->hw.mac.tx_pkt_filtering)
 		e1000_transfer_dhcp_info(adapter, skb);
@@ -5144,15 +5139,18 @@ static netdev_tx_t e1000_xmit_frame(struct sk_buff *skb,
 		tx_flags |= E1000_TX_FLAGS_NO_FCS;
 
 	/* if count is 0 then mapping error has occurred */
-	count = e1000_tx_map(tx_ring, skb, first, max_per_txd, nr_frags, mss);
+	count = e1000_tx_map(tx_ring, skb, first, adapter->tx_fifo_limit,
+			     nr_frags);
 	if (count) {
 		skb_tx_timestamp(skb);
 
 		netdev_sent_queue(netdev, skb->len);
 		e1000_tx_queue(tx_ring, tx_flags, count);
 		/* Make sure there is space in the ring for the next send. */
-		e1000_maybe_stop_tx(tx_ring, MAX_SKB_FRAGS + 2);
-
+		e1000_maybe_stop_tx(tx_ring,
+				    (MAX_SKB_FRAGS *
+				     DIV_ROUND_UP(PAGE_SIZE,
+						  adapter->tx_fifo_limit) + 2));
 	} else {
 		dev_kfree_skb_any(skb);
 		tx_ring->buffer_info[first].time_stamp = 0;
@@ -6327,8 +6325,8 @@ static int __devinit e1000_probe(struct pci_dev *pdev,
 	adapter->hw.phy.autoneg_advertised = 0x2f;
 
 	/* ring size defaults */
-	adapter->rx_ring->count = 256;
-	adapter->tx_ring->count = 256;
+	adapter->rx_ring->count = E1000_DEFAULT_RXD;
+	adapter->tx_ring->count = E1000_DEFAULT_TXD;
 
 	/*
 	 * Initial Wake on LAN setting - If APM wake is enabled in