OvmfPkg: enable CPU hotplug support in PiSmmCpuDxeSmm

Set "PcdCpuHotPlugSupport" to TRUE, when OVMF is built with SMM_REQUIRE.
Consequences:

(1) In PiCpuSmmEntry() [UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c],
    resources are allocated and populated in advance for all possible
    (i.e., potentially hot-added) processors, rather than only the
    processors present at boot.

    The possible count (called "mMaxNumberOfCpus") is set from
    "PcdCpuMaxLogicalProcessorNumber"; we set the latter in
    OvmfPkg/PlatformPei. (Refer to commit 83357313dd,
    "OvmfPkg/PlatformPei: rewrite MaxCpuCountInitialization() for CPU
    hotplug", 2020-01-29).

(2) The AddProcessor() and RemoveProcessor() member functions of
    EFI_SMM_CPU_SERVICE_PROTOCOL, implemented in
    "UefiCpuPkg/PiSmmCpuDxeSmm/CpuService.c", are no longer
    short-circuited to EFI_UNSUPPORTED.

    We'll rely on these functions in the CPU hotplug SMI handler, in a
    subsequent patch.

(3) In PiCpuSmmEntry(), the address of the CPU_HOT_PLUG_DATA structure (in
    SMRAM) is exposed via the dynamic-only "PcdCpuHotPlugDataAddress".

    This structure is an information channel between the CPU hotplug SMI
    handler, and EFI_SMM_CPU_SERVICE_PROTOCOL. Namely, at the first
    "Index" where the following equality holds:

      CPU_HOT_PLUG_DATA.ApicId[Index] == INVALID_APIC_ID

    a hot-plugged CPU can be accepted, with the steps below:

(3.1) The hotplug SMI handler has to overwrite INVALID_APIC_ID with the
      new CPU's APIC ID.

(3.2) The new CPU's SMBASE has to be relocated to:

        CPU_HOT_PLUG_DATA.SmBase[Index]

      (which was precomputed in step (1) above).

(3.3) The hotplug SMI handler is supposed to call
      EFI_SMM_CPU_SERVICE_PROTOCOL.AddProcessor().

Note: we need not spell out "PcdCpuHotPlugDataAddress" in the
[PcdsDynamicDefault] sections of the OVMF DSC files, just so the PCD
become dynamically settable. That's because "UefiCpuPkg.dec" declares this
PCD with [PcdsDynamic, PcdsDynamicEx] access methods *only*.

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: <20200226221156.29589-6-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

OvmfPkg/OvmfPkgIa32.dsc

@@ -437,6 +437,7 @@
 !endif
 !if $(SMM_REQUIRE) == TRUE
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire|TRUE
+  gUefiCpuPkgTokenSpaceGuid.PcdCpuHotPlugSupport|TRUE
   gEfiMdeModulePkgTokenSpaceGuid.PcdEnableVariableRuntimeCache|FALSE
 !endif
 

OvmfPkg/OvmfPkgIa32X64.dsc

@@ -441,6 +441,7 @@
 !endif
 !if $(SMM_REQUIRE) == TRUE
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire|TRUE
+  gUefiCpuPkgTokenSpaceGuid.PcdCpuHotPlugSupport|TRUE
   gEfiMdeModulePkgTokenSpaceGuid.PcdEnableVariableRuntimeCache|FALSE
 !endif
 

OvmfPkg/OvmfPkgX64.dsc

@@ -441,6 +441,7 @@
 !endif
 !if $(SMM_REQUIRE) == TRUE
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire|TRUE
+  gUefiCpuPkgTokenSpaceGuid.PcdCpuHotPlugSupport|TRUE
   gEfiMdeModulePkgTokenSpaceGuid.PcdEnableVariableRuntimeCache|FALSE
 !endif