[PATCH RFC v2 05/28] MdePkg: Add AsmPvalidate() support

["Brijesh Singh" <brijesh.singh@amd.com>]

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>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 MdePkg/Include/Library/BaseLib.h          | 37 +++++++++++++++++
 MdePkg/Library/BaseLib/BaseLib.inf        |  1 +
 MdePkg/Library/BaseLib/X64/Pvalidate.nasm | 43 ++++++++++++++++++++
 3 files changed, 81 insertions(+)

diff --git a/MdePkg/Include/Library/BaseLib.h b/MdePkg/Include/Library/BaseLib.h
index 7253997a6f..92ce695e93 100644
--- a/MdePkg/Include/Library/BaseLib.h
+++ b/MdePkg/Include/Library/BaseLib.h
@@ -7518,5 +7518,42 @@ PatchInstructionX86 (
   IN  UINTN                    ValueSize
   );
 
+/**
+ Execute a PVALIDATE instruction to validate or rescnids validation of a guest
+ page's RMP entry.
+
+ Upon completion, in addition to the return value the instruction also updates
+ the eFlags. A caller must check both the return code as well as eFlags to
+ determine if the RMP entry has been updated.
+
+ The function is available on x64.
+
+ @param[in]    Address        The guest virtual address to validate.
+ @param[in]    PageSize       The page size to use.
+ @param[i]     Validate       Validate or rescinds.
+ @param[out]   Eflags         The value of Eflags after PVALIDATE completion.
+
+ @retval       PvalidateRetValue  The return value from the PVALIDATE instruction.
+**/
+typedef enum {
+  PvalidatePageSize4K = 0,
+  PvalidatePageSize2MB,
+} PVALIDATE_PAGE_SIZE;
+
+typedef enum {
+  PvalidateRetSuccess = 0,
+  PvalidateRetFailInput = 1,
+  PvalidateRetFailSizemismatch = 6,
+} PVALIDATE_RET_VALUE;
+
+PVALIDATE_RET_VALUE
+EFIAPI
+AsmPvalidate (
+  IN   PVALIDATE_PAGE_SIZE     PageSize,
+  IN   BOOLEAN                 Validate,
+  IN   UINTN                   Address,
+  OUT  IA32_EFLAGS32           *Eflags
+  );
+
 #endif // defined (MDE_CPU_IA32) || defined (MDE_CPU_X64)
 #endif // !defined (__BASE_LIB__)
diff --git a/MdePkg/Library/BaseLib/BaseLib.inf b/MdePkg/Library/BaseLib/BaseLib.inf
index b76f3af380..d33b4a8f7d 100644
--- a/MdePkg/Library/BaseLib/BaseLib.inf
+++ b/MdePkg/Library/BaseLib/BaseLib.inf
@@ -321,6 +321,7 @@
   X64/XGetBv.nasm
   X64/XSetBv.nasm
   X64/VmgExit.nasm
+  X64/Pvalidate.nasm
   ChkStkGcc.c  | GCC
 
 [Sources.EBC]
diff --git a/MdePkg/Library/BaseLib/X64/Pvalidate.nasm b/MdePkg/Library/BaseLib/X64/Pvalidate.nasm
new file mode 100644
index 0000000000..f2aba114ac
--- /dev/null
+++ b/MdePkg/Library/BaseLib/X64/Pvalidate.nasm
@@ -0,0 +1,43 @@
+;-----------------------------------------------------------------------------
+;
+; Copyright (c) 2020-2021, AMD. All rights reserved.<BR>
+; SPDX-License-Identifier: BSD-2-Clause-Patent
+;
+; Module Name:
+;
+;   Pvalidate.Asm
+;
+; Abstract:
+;
+;   AsmPvalidate function
+;
+; Notes:
+;
+;-----------------------------------------------------------------------------
+
+    SECTION .text
+
+;-----------------------------------------------------------------------------
+;  PvalidateRetValue
+;  EFIAPI
+;  AsmPvalidate (
+;    IN   UINT32  RmpPageSize
+;    IN   UINT32  Validate,
+;    IN   UINTN   Address,
+;    OUT  UINTN  *Eflags,
+;    )
+;-----------------------------------------------------------------------------
+global ASM_PFX(AsmPvalidate)
+ASM_PFX(AsmPvalidate):
+  mov     rax, r8
+
+  ; PVALIDATE instruction opcode
+  DB      0xF2, 0x0F, 0x01, 0xFF
+
+  ; Read the Eflags
+  pushfq
+  pop     r8
+  mov     [r9], r8
+
+  ; The PVALIDATE instruction returns the status in rax register.
+  ret
-- 
2.17.1