[PATCH 3/4] x86/Hyper-V: Trigger crash enlightenment only once during system crash.

[ltykernel@gmail.com]

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

Hyper-V expects guest only triggers crash enlightenment.
The second crash notify will be ignored by Hyper-V.

Current code may trigger crash enlightenment during system
panic twice.
1) The enlightenment is triggered in hyperv_panic/die_event()
via hyperv_report_panic().
2) hv_kmsg_dump() reports kmsg to host via hyperv_report_panic_msg().

Fix it. If kmsg dump is registered successfully, just report
kmsg via hyperv_report_panic_msg() and not report register values
via hyperv_report_panic().

Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
---
 drivers/hv/vmbus_drv.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index b043efea092a..1787d6246251 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -55,7 +55,12 @@ static int hyperv_panic_event(struct notifier_block *nb, unsigned long val,
 
 	vmbus_initiate_unload(true);
 
-	if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE) {
+	/*
+	 * Crash notify only can be triggered once. If crash notify
+	 * message is available, just report kmsg to crash buffer.
+	 */
+	if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE
+	    && !hv_panic_page) {
 		regs = current_pt_regs();
 		hyperv_report_panic(regs, val);
 	}
@@ -68,7 +73,12 @@ static int hyperv_die_event(struct notifier_block *nb, unsigned long val,
 	struct die_args *die = (struct die_args *)args;
 	struct pt_regs *regs = die->regs;
 
-	hyperv_report_panic(regs, val);
+	/*
+	 * Crash notify only can be triggered once. If crash notify
+	 * message is available, just report kmsg to crash buffer.
+	 */
+	if (!hv_panic_page)
+		hyperv_report_panic(regs, val);
 	return NOTIFY_DONE;
 }
 
-- 
2.14.5