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

Sean Christopherson
2022-05-11T23:44:01Z

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 | 26 ++++++++++++++------------
1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index f9543a4e9b09..33c1f4883b27 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -533,27 +533,29 @@ static void nmi_shootdown_nop(int cpu, struct pt_regs *regs)
/* Nothing to do, the NMI shootdown handler disables virtualization. */
}

-/* 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. */
+ if (cpu_has_vmx())
+ __cpu_emergency_vmxoff();
+ else
+ cpu_emergency_svm_disable();

- /* Halt and exit VMX root operation on the other CPUs. */
+ /* Disable VMX/SVM and halt on other CPUs. */
nmi_shootdown_cpus(nmi_shootdown_nop);
}
}
@@ -590,7 +592,7 @@ 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);

--
2.36.0.512.ge40c2bad7a-goog