MdePkg/BaseLib: add support for PVALIDATE instruction

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275

The PVALIDATE instruction validates or rescinds validation of a guest
page RMP entry. Upon completion, a return code is stored in EAX, rFLAGS
bits OF, ZF, AF, PF and SF are set based on this return code. If the
instruction completed succesfully, the rFLAGS bit CF indicates if the
contents of the RMP entry were changed or not.

For more information about the instruction see AMD APM volume 3.

Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Message-Id: <20210519181949.6574-8-brijesh.singh@amd.com>

MdePkg/Library/BaseLib/BaseLib.inf

@@ -317,6 +317,7 @@
   X64/GccInlinePriv.c | GCC
   X64/EnableDisableInterrupts.nasm
   X64/DisablePaging64.nasm
+  X64/Pvalidate.nasm
   X64/RdRand.nasm
   X64/XGetBv.nasm
   X64/XSetBv.nasm

MdePkg/Library/BaseLib/X64/Pvalidate.nasm

@@ -0,0 +1,42 @@
+;-----------------------------------------------------------------------------
+;
+; Copyright (c) 2021, AMD. All rights reserved.<BR>
+; SPDX-License-Identifier: BSD-2-Clause-Patent
+;
+;-----------------------------------------------------------------------------
+
+%include "Nasm.inc"
+
+    SECTION .text
+
+;-----------------------------------------------------------------------------
+;  UINT32
+;  EFIAPI
+;  AsmPvalidate (
+;    IN   UINT32              PageSize
+;    IN   UINT32              Validate,
+;    IN   UINT64              Address
+;    )
+;-----------------------------------------------------------------------------
+global ASM_PFX(AsmPvalidate)
+ASM_PFX(AsmPvalidate):
+  mov     rax, r8
+
+  PVALIDATE
+
+  ; Save the carry flag.
+  setc    dl
+
+  ; The PVALIDATE instruction returns the status in rax register.
+  cmp     rax, 0
+  jne     PvalidateExit
+
+  ; Check the carry flag to determine if RMP entry was updated.
+  cmp     dl, 0
+  je      PvalidateExit
+
+  ; Return the PVALIDATE_RET_NO_RMPUPDATE.
+  mov     rax, 255
+
+PvalidateExit:
+  ret