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

Sean Christopherson
2023-05-12T23:51:08Z

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