OvmfPkg/CpuHotplugSmm: collect CPUs with events

Call QemuCpuhpCollectApicIds() in the root MMI handler. The APIC IDs of
the hotplugged CPUs will be used for several purposes in subsequent
patches.

For calling QemuCpuhpCollectApicIds(), pre-allocate both of its output
arrays "PluggedApicIds" and "ToUnplugApicIds" in the driver's entry point
function. The allocation size is dictated by the possible CPU count, which
we fetch from "CPU_HOT_PLUG_DATA.ArrayLength".

The CPU_HOT_PLUG_DATA structure in SMRAM is an out-of-band information
channel between this driver and PiSmmCpuDxeSmm, underlying
EFI_SMM_CPU_SERVICE_PROTOCOL.

In order to consume "CPU_HOT_PLUG_DATA.ArrayLength", extend the driver's
DEPEX to EFI_SMM_CPU_SERVICE_PROTOCOL. PiSmmCpuDxeSmm stores the address
of CPU_HOT_PLUG_DATA to "PcdCpuHotPlugDataAddress", before it produces
EFI_SMM_CPU_SERVICE_PROTOCOL.

Stash the protocol at once, as it will be needed later.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1512
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200226221156.29589-11-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

OvmfPkg/CpuHotplugSmm/CpuHotplugSmm.inf

@@ -30,22 +30,27 @@
 [Packages]
   MdePkg/MdePkg.dec
   OvmfPkg/OvmfPkg.dec
+  UefiCpuPkg/UefiCpuPkg.dec
 
 [LibraryClasses]
   BaseLib
   DebugLib
   MmServicesTableLib
   PcdLib
+  SafeIntLib
   UefiDriverEntryPoint
 
 [Protocols]
   gEfiMmCpuIoProtocolGuid                                           ## CONSUMES
+  gEfiSmmCpuServiceProtocolGuid                                     ## CONSUMES
 
 [Pcd]
+  gUefiCpuPkgTokenSpaceGuid.PcdCpuHotPlugDataAddress                ## CONSUMES
   gUefiOvmfPkgTokenSpaceGuid.PcdQ35SmramAtDefaultSmbase             ## CONSUMES
 
 [FeaturePcd]
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire                     ## CONSUMES
 
 [Depex]
-  gEfiMmCpuIoProtocolGuid
+  gEfiMmCpuIoProtocolGuid AND
+  gEfiSmmCpuServiceProtocolGuid