In order to reproduce the problem, users just need to set the kernel
parameter "crash_kexec_post_notifiers" *without* kdump set in any
system with the VMX feature present.

Since there is no benefit in re-disabling VMX in all CPUs in case
it was already done, this patch prevents that by guarding the restart
routine against doubly issuing NMIs unnecessarily. Notice we still
need to disable VMX locally in the emergency restart.

Fixes: ed72736183c4 ("x86/reboot: Force all cpus to exit VMX root if VMX is supported)
Fixes: 0ee59413c967 ("x86/panic: replace smp_send_stop() with kdump friendly version in panic path")
Cc: David P. Reed <redacted>
Cc: Hidehiro Kawai <redacted>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
---
 arch/x86/include/asm/cpu.h |  1 +
 arch/x86/kernel/crash.c    |  8 ++++----
 arch/x86/kernel/reboot.c   | 14 ++++++++++++--
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index 86e5e4e26fcb..b6a9062d387f 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h

@@ -36,6 +36,7 @@ extern int _debug_hotplug_cpu(int cpu, int action);
 #endif
 #endif
 
+extern bool crash_cpus_stopped;
 int mwait_usable(const struct cpuinfo_x86 *);
 
 unsigned int x86_family(unsigned int sig);

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index e8326a8d1c5d..71dd1a990e8d 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c

@@ -42,6 +42,8 @@
 #include <asm/crash.h>
 #include <asm/cmdline.h>
 
+bool crash_cpus_stopped;
+
 /* Used while preparing memory map entries for second kernel */
 struct crash_memmap_data {
 	struct boot_params *params;

@@ -108,9 +110,7 @@ void kdump_nmi_shootdown_cpus(void)
 /* Override the weak function in kernel/panic.c */
 void crash_smp_send_stop(void)
 {
-	static int cpus_stopped;
-
-	if (cpus_stopped)
+	if (crash_cpus_stopped)
 		return;
 
 	if (smp_ops.crash_stop_other_cpus)

@@ -118,7 +118,7 @@ void crash_smp_send_stop(void)
 	else
 		smp_send_stop();
 
-	cpus_stopped = 1;
+	crash_cpus_stopped = true;

 }
 
 #else

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index fa700b46588e..2fc42b8402ac 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c

@@ -589,8 +589,18 @@ static void native_machine_emergency_restart(void)
 	int orig_reboot_type = reboot_type;
 	unsigned short mode;
 
-	if (reboot_emergency)
-		emergency_vmx_disable_all();
+	/*
+	 * We can reach this point in the end of panic path, having
+	 * NMI-disabled all secondary CPUs. This process involves
+	 * disabling the CPU virtualization technologies, so if that
+	 * is the case, we only miss disabling the local CPU VMX...
+	 */
+	if (reboot_emergency) {
+		if (!crash_cpus_stopped)
+			emergency_vmx_disable_all();
+		else
+			cpu_emergency_vmxoff();
+	}
 
 	tboot_shutdown(TB_SHUTDOWN_REBOOT);
 

-- 
2.36.0