[PATCH v3 06/18] x86/reboot: Assert that IRQs are disabled when turning off virtualization

[Sean Christopherson <seanjc@google.com>]

Assert that IRQs are disabled when turning off virtualization in an
emergency.  KVM enables hardware via on_each_cpu(), i.e. could re-enable
hardware if a pending IPI were delivered after disabling virtualization.

Remove a misleading comment from emergency_reboot_disable_virtualization()
about "just" needing to guarantee the CPU is stable (see above).

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kernel/reboot.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 20f7bdabc52e..fddfea5f1d20 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -531,7 +531,6 @@ static inline void nmi_shootdown_cpus_on_restart(void);
 
 static void emergency_reboot_disable_virtualization(void)
 {
-	/* Just make sure we won't change CPUs while doing this */
 	local_irq_disable();
 
 	/*
@@ -820,6 +819,13 @@ void cpu_emergency_disable_virtualization(void)
 {
 	cpu_emergency_virt_cb *callback;
 
+	/*
+	 * IRQs must be disabled as KVM enables virtualization in hardware via
+	 * function call IPIs, i.e. IRQs need to be disabled to guarantee
+	 * virtualization stays disabled.
+	 */
+	lockdep_assert_irqs_disabled();
+
 	rcu_read_lock();
 	callback = rcu_dereference(cpu_emergency_virt_callback);
 	if (callback)
-- 
2.40.1.606.ga4b1b128d6-goog