Xen appears to leave the BSP with STM on after it aborts STM launch due to an error on Protect Resources. It should teardown the BSP to not leave some CPU threads with STM on and some with STM off.
(XEN) XEN-STM: IgnoreResource: 0000
(XEN) XEN-STM: ResourceListContinuation : 0000000000000000
(XEN) STM: Reached end of BIOS Resource list
(XEN) STM: Protecting Xen Resources
(STM) STM_API_PROTECT_RESOURCE:
(XEN) STM: STM_API_PROTECT_RESOURCE failed with error: 0x8001000d
(XEN) STM: STM_API_PROTECT_RESOURCE return status in Hdr: 0
(XEN) STM: Exiting STM opt-in
(XEN) build-id: a507c4165535a6ea1cdea9107f10b820
(XEN) ACPI sleep modes: S3
protectresource-log.txt