[PATCH 0/4] x86/Hyper-V: Unload vmbus channel in hv panic callback

[ltykernel@gmail.com]

From: Tianyu Lan <Tianyu.Lan@microsoft.com>

Customer reported Hyper-V VM still responded network traffic
ack packets after kernel panic with kernel parameter "panic=0”.
This becauses vmbus driver interrupt handler still works
on the panic cpu after kernel panic. Panic cpu falls into
infinite loop of panic() with interrupt enabled at that point.
Vmbus driver can still handle network traffic.

This confuses remote service that the panic system is still
alive when it gets ack packets. Unload vmbus channel in hv panic
callback and fix it.

vmbus_initiate_unload() maybe double called during panic process
(e.g, hyperv_panic_event() and hv_crash_handler()). So check
and set connection state in vmbus_initiate_unload() to resolve
reenter issue.

Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
---
 drivers/hv/channel_mgmt.c |  5 +++++
 drivers/hv/vmbus_drv.c    | 17 +++++++++--------
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 0370364169c4..893493f2b420 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -839,6 +839,9 @@ void vmbus_initiate_unload(bool crash)
 {
 	struct vmbus_channel_message_header hdr;
 
+	if (vmbus_connection.conn_state == DISCONNECTED)
+		return;
+
 	/* Pre-Win2012R2 hosts don't support reconnect */
 	if (vmbus_proto_version < VERSION_WIN8_1)
 		return;
@@ -857,6 +860,8 @@ void vmbus_initiate_unload(bool crash)
 		wait_for_completion(&vmbus_connection.unload_event);
 	else
 		vmbus_wait_for_unload();
+
+	vmbus_connection.conn_state = DISCONNECTED;
 }
 
 static void check_ready_for_resume_event(void)
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 029378c27421..b56b9fb9bd90 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -53,9 +53,12 @@ static int hyperv_panic_event(struct notifier_block *nb, unsigned long val,
 {
 	struct pt_regs *regs;
 
-	regs = current_pt_regs();
+	vmbus_initiate_unload(true);
 
-	hyperv_report_panic(regs, val);
+	if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE) {
+		regs = current_pt_regs();
+		hyperv_report_panic(regs, val);
+	}
 	return NOTIFY_DONE;
 }
 
@@ -1391,10 +1394,12 @@ static int vmbus_bus_init(void)
 		}
 
 		register_die_notifier(&hyperv_die_block);
-		atomic_notifier_chain_register(&panic_notifier_list,
-					       &hyperv_panic_block);
 	}
 
+	/* Vmbus channel is unloaded in panic callback when panic happens.*/
+	atomic_notifier_chain_register(&panic_notifier_list,
+			       &hyperv_panic_block);
+
 	vmbus_request_offers();
 
 	return 0;
@@ -2204,8 +2209,6 @@ static int vmbus_bus_suspend(struct device *dev)
 
 	vmbus_initiate_unload(false);
 
-	vmbus_connection.conn_state = DISCONNECTED;
-
 	/* Reset the event for the next resume. */
 	reinit_completion(&vmbus_connection.ready_for_resume_event);
 
@@ -2289,7 +2292,6 @@ static void hv_kexec_handler(void)
 {
 	hv_stimer_global_cleanup();
 	vmbus_initiate_unload(false);
-	vmbus_connection.conn_state = DISCONNECTED;
 	/* Make sure conn_state is set as hv_synic_cleanup checks for it */
 	mb();
 	cpuhp_remove_state(hyperv_cpuhp_online);
@@ -2306,7 +2308,6 @@ static void hv_crash_handler(struct pt_regs *regs)
 	 * doing the cleanup for current CPU only. This should be sufficient
 	 * for kdump.
 	 */
-	vmbus_connection.conn_state = DISCONNECTED;
 	cpu = smp_processor_id();
 	hv_stimer_cleanup(cpu);
 	hv_synic_disable_regs(cpu);
-- 
2.14.5