OvmfPkg/CpuHotplugSmm: introduce Post-SMM Pen for hot-added CPUs

Once a hot-added CPU finishes the SMBASE relocation, we need to pen it in
a HLT loop. Add the NASM implementation (with just a handful of
instructions, but much documentation), and some C language helper
functions.

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: <20200226221156.29589-12-lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

OvmfPkg/CpuHotplugSmm/Smbase.h

@@ -0,0 +1,32 @@
+/** @file
+  SMBASE relocation for hot-plugged CPUs.
+
+  Copyright (c) 2020, Red Hat, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#ifndef SMBASE_H_
+#define SMBASE_H_
+
+#include <Uefi/UefiBaseType.h> // EFI_STATUS
+#include <Uefi/UefiSpec.h>     // EFI_BOOT_SERVICES
+
+EFI_STATUS
+SmbaseAllocatePostSmmPen (
+  OUT UINT32                  *PenAddress,
+  IN  CONST EFI_BOOT_SERVICES *BootServices
+  );
+
+VOID
+SmbaseReinstallPostSmmPen (
+  IN UINT32 PenAddress
+  );
+
+VOID
+SmbaseReleasePostSmmPen (
+  IN UINT32                  PenAddress,
+  IN CONST EFI_BOOT_SERVICES *BootServices
+  );
+
+#endif // SMBASE_H_