Commit ad93c1a7 authored Jul 21, 2023 by Sean Christopherson

x86/reboot: Assert that IRQs are disabled when turning off virtualization

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).

Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20230721201859.2307736-6-seanjc@google.com

Signed-off-by: Sean Christopherson <seanjc@google.com>

parent baeb4de7

arch/x86/kernel/reboot.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -532,7 +532,6 @@ 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();

		/*
		@@ -821,6 +820,13 @@ 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)