[PATCH v3 2/3] x86/reboot: Disable virtualization in an emergency if SVM is supported

[Sean Christopherson <seanjc@google.com>]

Disable SVM on all CPUs via NMI shootdown during an emergency reboot.
Like VMX, SVM can block INIT and thus prevent bringing up other CPUs via
INIT-SIPI-SIPI.

Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kernel/reboot.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index f2655b78d73c..973a1b2c61bf 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -530,27 +530,26 @@ static inline void kb_wait(void)
 
 static inline void nmi_shootdown_cpus_on_restart(void);
 
-/* Use NMIs as IPIs to tell all CPUs to disable virtualization */
-static void emergency_vmx_disable_all(void)
+static void emergency_reboot_disable_virtualization(void)
 {
 	/* Just make sure we won't change CPUs while doing this */
 	local_irq_disable();
 
 	/*
-	 * Disable VMX on all CPUs before rebooting, otherwise we risk hanging
-	 * the machine, because the CPU blocks INIT when it's in VMX root.
+	 * Disable virtualization on all CPUs before rebooting to avoid hanging
+	 * the system, as VMX and SVM block INIT when running in the host.
 	 *
 	 * We can't take any locks and we may be on an inconsistent state, so
-	 * use NMIs as IPIs to tell the other CPUs to exit VMX root and halt.
+	 * use NMIs as IPIs to tell the other CPUs to disable VMX/SVM and halt.
 	 *
-	 * Do the NMI shootdown even if VMX if off on _this_ CPU, as that
-	 * doesn't prevent a different CPU from being in VMX root operation.
+	 * Do the NMI shootdown even if virtualization is off on _this_ CPU, as
+	 * other CPUs may have virtualization enabled.
 	 */
-	if (cpu_has_vmx()) {
-		/* Safely force _this_ CPU out of VMX root operation. */
-		__cpu_emergency_vmxoff();
+	if (cpu_has_vmx() || cpu_has_svm(NULL)) {
+		/* Safely force _this_ CPU out of VMX/SVM operation. */
+		cpu_crash_disable_virtualization();
 
-		/* Halt and exit VMX root operation on the other CPUs. */
+		/* Disable VMX/SVM and halt on other CPUs. */
 		nmi_shootdown_cpus_on_restart();
 	}
 }
@@ -587,7 +586,7 @@ static void native_machine_emergency_restart(void)
 	unsigned short mode;
 
 	if (reboot_emergency)
-		emergency_vmx_disable_all();
+		emergency_reboot_disable_virtualization();
 
 	tboot_shutdown(TB_SHUTDOWN_REBOOT);
 
-- 
2.38.1.431.g37b22c650d-goog