For CPU with VMX feature, if there's no crash kernel loaded and
crash_kexec_post_notifiers is true, then it will endup call
nmi_shootdown_cpus() twice. This will crash the system because it double
register the same nmi callback

The first call is:

    nmi_shootdown_cpus+0x21/0xc0
    kdump_nmi_shootdown_cpus+0x15/0x20
    crash_smp_send_stop+0x23/0x40
    __panic+0xec/0x2d0

The second call is:

    nmi_shootdown_cpus+0x21/0xc0
    native_machine_emergency_restart+0x7d/0x270
    machine_emergency_restart+0x1c/0x20
    emergency_restart+0x1a/0x20
    __panic+0x231/0x2d0

Fixes: d176720d34c7 ("x86: disable VMX on all CPUs on reboot")
Fixes: 2340b62f77c7 ("kdump: forcibly disable VMX and SVM on machine_crash_shutdown()")
Signed-off-by: Weinan Liu <wnliu@google.com>
---
 arch/x86/kernel/reboot.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index c3636ea4aa71..f9890e299750 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -837,7 +837,17 @@ static int crash_nmi_callback(unsigned int val, struct pt_regs *regs)
  */
 void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 {
+	static bool cpus_shutdown;
 	unsigned long msecs;
+
+	/*
+	 * Only shutdown CPUs once. Double register nmi callback will crash the
+	 * system
+	 */
+	if (cpus_shutdown)
+		return;
+	cpus_shutdown = true;
+
 	local_irq_disable();
 
 	/* Make a note of crashing cpu. Will be used in NMI callback. */
-- 
2.37.1.595.g718a3a8f04-goog