[PATCH V2 3/6] x86/Hyper-V: Trigger crash enlightenment only once during system crash.

[ltykernel]

From: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>

When a guest VM panics, Hyper-V should be notified only once via the
crash synthetic MSRs.  Current Linux code might write these crash MSRs
twice during a system panic:
1) hyperv_panic/die_event() calling hyperv_report_panic()
2) hv_kmsg_dump() calling hyperv_report_panic_msg()

Fix this by not calling hyperv_report_panic() if a kmsg dump has been
successfully registered.  The notification will happen later via
hyperv_report_panic_msg().

Signed-off-by: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
---
Change since v1:
	- Update commit log
---
 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 3a0472c8b7ae..d73fa8aa00a3 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