netdev - [PATCH iwl-net v2] ice: reset first in crash dump kernels

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Date: Mon,  2 Oct 2023 13:02:32 -0700
From: Jesse Brandeburg <jesse.brandeburg@...el.com>
To: intel-wired-lan@...ts.osuosl.org
Cc: Jesse Brandeburg <jesse.brandeburg@...el.com>,
	linux-pci@...r.kernel.org,
	pmenzel@...gen.mpg.de,
	netdev@...r.kernel.org,
	jkc@...hat.com,
	Vishal Agrawal <vagrawal@...hat.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>
Subject: [PATCH iwl-net v2] ice: reset first in crash dump kernels

When the system boots into the crash dump kernel after a panic, the ice
networking device may still have pending transactions that can cause errors
or machine checks when the device is re-enabled. This can prevent the crash
dump kernel from loading the driver or collecting the crash data.

To avoid this issue, perform a function level reset (FLR) on the ice device
via PCIe config space before enabling it on the crash kernel. This will
clear any outstanding transactions and stop all queues and interrupts.
Restore the config space after the FLR, otherwise it was found in testing
that the driver wouldn't load successfully.

The following sequence causes the original issue:
- Load the ice driver with modprobe ice
- Enable SR-IOV with 2 VFs: echo 2 > /sys/class/net/eth0/device/sriov_num_vfs
- Trigger a crash with echo c > /proc/sysrq-trigger
- Load the ice driver again (or let it load automatically) with modprobe ice
- The system crashes again during pcim_enable_device()

Reported-by: Vishal Agrawal <vagrawal@...hat.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
---
v2: respond to list comments and update commit message
v1: initial version
---
 drivers/net/ethernet/intel/ice/ice_main.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/net/ethernet/intel/ice/ice_main.c b/drivers/net/ethernet/intel/ice/ice_main.c
index c8286adae946..6550c46e4e36 100644
--- a/drivers/net/ethernet/intel/ice/ice_main.c
+++ b/drivers/net/ethernet/intel/ice/ice_main.c
@@ -6,6 +6,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <generated/utsrelease.h>
+#include <linux/crash_dump.h>
 #include "ice.h"
 #include "ice_base.h"
 #include "ice_lib.h"
@@ -5014,6 +5015,20 @@ ice_probe(struct pci_dev *pdev, const struct pci_device_id __always_unused *ent)
 		return -EINVAL;
 	}
 
+	/* when under a kdump kernel initiate a reset before enabling the
+	 * device in order to clear out any pending DMA transactions. These
+	 * transactions can cause some systems to machine check when doing
+	 * the pcim_enable_device() below.
+	 */
+	if (is_kdump_kernel()) {
+		pci_save_state(pdev);
+		pci_clear_master(pdev);
+		err = pcie_flr(pdev);
+		if (err)
+			return err;
+		pci_restore_state(pdev);
+	}
+
 	/* this driver uses devres, see
 	 * Documentation/driver-api/driver-model/devres.rst
 	 */

base-commit: 6a70e5cbedaf8ad10528ac9ac114f3ec20f422df
-- 
2.39.3