From: Tianyu Lan <Tianyu.Lan@microsoft.com>
Date: Mon, 6 Apr 2020 08:53:28 -0700
Patch-mainline: v5.7-rc2
Subject: x86/Hyper-V: Trigger crash enlightenment only once during system crash.
Git-commit: 73f26e526f19afb3a06b76b970a76bcac2cafd05
References: bsc#1170617, bsc#1170618

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().

Fixes: 7ed4325a44ea ("Drivers: hv: vmbus: Make panic reporting to be more useful")
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Link: https://lore.kernel.org/r/20200406155331.2105-4-Tianyu.Lan@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Acked-by: Olaf Hering <ohering@suse.de>
---
 drivers/hv/vmbus_drv.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -55,7 +55,13 @@ 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) {
+	/*
+	 * Hyper-V should be notified only once about a panic.  If we will be
+	 * doing hyperv_report_panic_msg() later with kmsg data, don't do
+	 * the notification here.
+	 */
+	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 +74,13 @@ 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);
+	/*
+	 * Hyper-V should be notified only once about a panic.  If we will be
+	 * doing hyperv_report_panic_msg() later with kmsg data, don't do
+	 * the notification here.
+	 */
+	if (!hv_panic_page)
+		hyperv_report_panic(regs, val);
 	return NOTIFY_DONE;
 }