[PATCH net 2/4] igc: fix page fault in XDP TX timestamps handling

[Tony Nguyen <anthony.l.nguyen@intel.com>]

From: Zdenek Bouska <zdenek.bouska@siemens.com>

If an XDP application that requested TX timestamping is shutting down
while the link of the interface in use is still up the following kernel
splat is reported:

[  883.803618] [   T1554] BUG: unable to handle page fault for address: ffffcfb6200fd008
...
[  883.803650] [   T1554] Call Trace:
[  883.803652] [   T1554]  <TASK>
[  883.803654] [   T1554]  igc_ptp_tx_tstamp_event+0xdf/0x160 [igc]
[  883.803660] [   T1554]  igc_tsync_interrupt+0x2d5/0x300 [igc]
...

During shutdown of the TX ring the xsk_meta pointers are left behind, so
that the IRQ handler is trying to touch them.

This issue is now being fixed by cleaning up the stale xsk meta data on
TX shutdown. TX timestamps on other queues remain unaffected.

Fixes: 15fd021bc427 ("igc: Add Tx hardware timestamp request for AF_XDP zero-copy packet")
Signed-off-by: Zdenek Bouska <zdenek.bouska@siemens.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-by: Florian Bezdeka <florian.bezdeka@siemens.com>
Tested-by: Avigail Dahan <avigailx.dahan@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
---
 drivers/net/ethernet/intel/igc/igc.h      |  2 ++
 drivers/net/ethernet/intel/igc/igc_main.c |  7 +++++
 drivers/net/ethernet/intel/igc/igc_ptp.c  | 33 +++++++++++++++++++++++
 3 files changed, 42 insertions(+)

diff --git a/drivers/net/ethernet/intel/igc/igc.h b/drivers/net/ethernet/intel/igc/igc.h
index a427f05814c1..17236813965d 100644
--- a/drivers/net/ethernet/intel/igc/igc.h
+++ b/drivers/net/ethernet/intel/igc/igc.h
@@ -781,6 +781,8 @@ int igc_ptp_hwtstamp_set(struct net_device *netdev,
 			 struct kernel_hwtstamp_config *config,
 			 struct netlink_ext_ack *extack);
 void igc_ptp_tx_hang(struct igc_adapter *adapter);
+void igc_ptp_clear_xsk_tx_tstamp_queue(struct igc_adapter *adapter,
+				       u16 queue_id);
 void igc_ptp_read(struct igc_adapter *adapter, struct timespec64 *ts);
 void igc_ptp_tx_tstamp_event(struct igc_adapter *adapter);
 
diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 1c5d7b23f225..72bc5128d8b8 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -264,6 +264,13 @@ static void igc_clean_tx_ring(struct igc_ring *tx_ring)
 	/* reset next_to_use and next_to_clean */
 	tx_ring->next_to_use = 0;
 	tx_ring->next_to_clean = 0;
+
+	/* Clear any lingering XSK TX timestamp requests */
+	if (test_bit(IGC_RING_FLAG_TX_HWTSTAMP, &tx_ring->flags)) {
+		struct igc_adapter *adapter = netdev_priv(tx_ring->netdev);
+
+		igc_ptp_clear_xsk_tx_tstamp_queue(adapter, tx_ring->queue_index);
+	}
 }
 
 /**
diff --git a/drivers/net/ethernet/intel/igc/igc_ptp.c b/drivers/net/ethernet/intel/igc/igc_ptp.c
index 44ee19386766..3d6b2264164a 100644
--- a/drivers/net/ethernet/intel/igc/igc_ptp.c
+++ b/drivers/net/ethernet/intel/igc/igc_ptp.c
@@ -577,6 +577,39 @@ static void igc_ptp_clear_tx_tstamp(struct igc_adapter *adapter)
 	spin_unlock_irqrestore(&adapter->ptp_tx_lock, flags);
 }
 
+/**
+ * igc_ptp_clear_xsk_tx_tstamp_queue - Clear pending XSK TX timestamps for a queue
+ * @adapter: Board private structure
+ * @queue_id: TX queue index to clear timestamps for
+ *
+ * Iterates over all TX timestamp registers and releases any pending
+ * timestamp requests associated with the given TX queue. This is
+ * called when an XDP pool is being disabled to ensure no stale
+ * timestamp references remain.
+ */
+void igc_ptp_clear_xsk_tx_tstamp_queue(struct igc_adapter *adapter, u16 queue_id)
+{
+	unsigned long flags;
+	int i;
+
+	spin_lock_irqsave(&adapter->ptp_tx_lock, flags);
+
+	for (i = 0; i < IGC_MAX_TX_TSTAMP_REGS; i++) {
+		struct igc_tx_timestamp_request *tstamp = &adapter->tx_tstamp[i];
+
+		if (tstamp->buffer_type != IGC_TX_BUFFER_TYPE_XSK)
+			continue;
+		if (tstamp->xsk_queue_index != queue_id)
+			continue;
+		if (!tstamp->xsk_tx_buffer)
+			continue;
+
+		igc_ptp_free_tx_buffer(adapter, tstamp);
+	}
+
+	spin_unlock_irqrestore(&adapter->ptp_tx_lock, flags);
+}
+
 static void igc_ptp_disable_tx_timestamp(struct igc_adapter *adapter)
 {
 	struct igc_hw *hw = &adapter->hw;
-- 
2.47.1