[PATCH] UefiCpuPkg/ResetVector:Add Option to reserve 4K region at 4GB

["cbduggap" <chinni.b.duggapu@intel.com>]

From: "Duggapu, Chinni B" <chinni.b.duggapu@intel.com>

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4140

Some implementations may need to keep the initial Reset code to be
separated out from rest of the code.This request is to add padding at
lower 4K region below 4 GB which will result having only few jmp
instructions and data at that region.

Cc: Ray Ni <ray.ni@intel.com>
Signed-off-by: Duggapu Chinni B <chinni.b.duggapu@intel.com>
---
 UefiCpuPkg/ResetVector/Vtf0/Ia16/ResetVectorVtf0.asm | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/UefiCpuPkg/ResetVector/Vtf0/Ia16/ResetVectorVtf0.asm b/UefiCpuPkg/ResetVector/Vtf0/Ia16/ResetVectorVtf0.asm
index 7538192876..fe5bbea803 100644
--- a/UefiCpuPkg/ResetVector/Vtf0/Ia16/ResetVectorVtf0.asm
+++ b/UefiCpuPkg/ResetVector/Vtf0/Ia16/ResetVectorVtf0.asm
@@ -21,7 +21,15 @@ ALIGN   16
 ; located just below 0x100000000 (4GB) in the firmware device.
 ;
 %ifdef ALIGN_TOP_TO_4K_FOR_PAGING
-    TIMES (0x1000 - ($ - EndOfPageTables) - 0x20) DB 0
+    TIMES (0x1000 - ($ - EndOfPageTables)) DB 0
+;
+; Pad the VTF0 Reset code for Bsp & Ap to 4k aligned block.
+; Some implementations may need to keep the initial Reset code
+; to be separated out from rest of the code.
+; This padding will make sure lower 4K region below 4 GB may
+; only contains few jmp instructions and data.
+;
+    TIMES (0x1000 - 0x20) DB 0
 %endif
 
 applicationProcessorEntryPoint:
-- 
2.30.2.windows.1