The ICH9_LPC_SMI_F_BROADCAST and ICH9_LPC_SMI_F_CPU_HOTPLUG feature flags
cause QEMU to behave as follows:
BROADCAST CPU_HOTPLUG use case / behavior
--------- ----------- ------------------------------------------------
clear clear OVMF built without SMM_REQUIRE; or very old OVMF
(from before commit a316d7ac91 / 2017-02-07).
QEMU permits CPU hotplug operations, and does
not cause the OS to inject an SMI upon hotplug.
Firmware is not expected to be aware of hotplug
events.
clear set Invalid feature set; QEMU rejects the feature
negotiation.
set clear OVMF after a316d7ac91 / 2017-02-07, built with
SMM_REQUIRE, but no support for CPU hotplug.
QEMU gracefully refuses hotplug operations.
set set OVMF after a316d7ac91 / 2017-02-07, built with
SMM_REQUIRE, and supporting CPU hotplug. QEMU
permits CPU hotplug operations, and causes the
OS to inject an SMI upon hotplug. Firmware is
expected to deal with hotplug events.
Negotiate ICH9_LPC_SMI_F_CPU_HOTPLUG -- but only if SEV is disabled, as
OvmfPkg/CpuHotplugSmm can't deal with SEV yet.
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Liran Alon <liran.alon@oracle.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200714184305.9814-1-lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
5ba203b54e