From: Sean Christopherson <seanjc@xxxxxxxxxx>
commit ed72736183c45a413a8d6974dd04be90f514cb6b upstream.
Force all CPUs to do VMXOFF (via NMI shootdown) during an emergency
reboot if VMX is _supported_, as VMX being off on the current CPU does
not prevent other CPUs from being in VMX root (post-VMXON). This fixes
a bug where a crash/panic reboot could leave other CPUs in VMX root and
prevent them from being woken via INIT-SIPI-SIPI in the new kernel.
Fixes: d176720d34c7 ("x86: disable VMX on all CPUs on reboot")
Cc: stable@xxxxxxxxxxxxxxx
Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: David P. Reed <dpreed@xxxxxxxxxxxx>
[sean: reworked changelog and further tweaked comment]
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20201231002702.2223707-3-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/reboot.c | 29 ++++++++++-------------------
1 file changed, 10 insertions(+), 19 deletions(-)
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -538,29 +538,20 @@ static void emergency_vmx_disable_all(vo
local_irq_disable();
/*
- * We need to disable VMX on all CPUs before rebooting, otherwise
- * we risk hanging up the machine, because the CPU ignore INIT
- * signals when VMX is enabled.
+ * Disable VMX on all CPUs before rebooting, otherwise we risk hanging
+ * the machine, because the CPU blocks INIT when it's in VMX root.
*
- * We can't take any locks and we may be on an inconsistent
- * state, so we use NMIs as IPIs to tell the other CPUs to disable
- * VMX and halt.
+ * 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.
*
- * For safety, we will avoid running the nmi_shootdown_cpus()
- * stuff unnecessarily, but we don't have a way to check
- * if other CPUs have VMX enabled. So we will call it only if the
- * CPU we are running on has VMX enabled.
- *
- * We will miss cases where VMX is not enabled on all CPUs. This
- * shouldn't do much harm because KVM always enable VMX on all
- * CPUs anyway. But we can miss it on the small window where KVM
- * is still enabling VMX.
+ * 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.
*/
- if (cpu_has_vmx() && cpu_vmx_enabled()) {
- /* Disable VMX on this CPU. */
- cpu_vmxoff();
+ if (cpu_has_vmx()) {
+ /* Safely force _this_ CPU out of VMX root operation. */
+ __cpu_emergency_vmxoff();
- /* Halt and disable VMX on the other CPUs */
+ /* Halt and exit VMX root operation on the other CPUs. */
nmi_shootdown_cpus(vmxoff_nmi);
}
