OvmfPkg/CpuHotplugSmm: add EjectCpu()

Add EjectCpu(), which handles the CPU ejection, and provides a holding
area for said CPUs. It is called via SmmCpuFeaturesRendezvousExit(),
at the tail end of the SMI handling.

Also UnplugCpus() now stashes QEMU Selectors of CPUs which need to be
ejected in CPU_HOT_EJECT_DATA.QemuSelectorMap. This is used by
EjectCpu() to identify CPUs marked for ejection.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Aaron Young <aaron.young@oracle.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3132
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Message-Id: <20210312062656.2477515-9-ankur.a.arora@oracle.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>

OvmfPkg/CpuHotplugSmm/CpuHotplugSmm.inf

@@ -40,6 +40,7 @@
 [LibraryClasses]
   BaseLib
   BaseMemoryLib
+  CpuLib
   DebugLib
   LocalApicLib
   MmServicesTableLib
@@ -54,6 +55,7 @@
 
 [Pcd]
   gUefiCpuPkgTokenSpaceGuid.PcdCpuHotPlugDataAddress                ## CONSUMES
+  gUefiOvmfPkgTokenSpaceGuid.PcdCpuHotEjectDataAddress              ## CONSUMES
   gUefiOvmfPkgTokenSpaceGuid.PcdQ35SmramAtDefaultSmbase             ## CONSUMES
 
 [FeaturePcd]