1 files changed, 94 insertions, 0 deletions
diff --git a/MdePkg/Library/BaseLib/X64/VmgExitSvsm.nasm b/MdePkg/Library/BaseLib/X64/VmgExitSvsm.nasm
new file mode 100644
index 0000000000..b8af788906
--- /dev/null
+++ b/MdePkg/Library/BaseLib/X64/VmgExitSvsm.nasm
@@ -0,0 +1,94 @@
+;------------------------------------------------------------------------------
+;
+; Copyright (C) 2024, Advanced Micro Devices, Inc. All rights reserved.<BR>
+; SPDX-License-Identifier: BSD-2-Clause-Patent
+;
+; Module Name:
+;
+;   VmgExitSvsm.Asm
+;
+; Abstract:
+;
+;   AsmVmgExitSvsm function
+;
+; Notes:
+;
+;------------------------------------------------------------------------------
+
+    DEFAULT REL
+    SECTION .text
+
+;------------------------------------------------------------------------------
+; typedef struct {
+;   VOID      *Caa;
+;   UINT64    RaxIn;
+;   UINT64    RcxIn;
+;   UINT64    RdxIn;
+;   UINT64    R8In;
+;   UINT64    R9In;
+;   UINT64    RaxOut;
+;   UINT64    RcxOut;
+;   UINT64    RdxOut;
+;   UINT64    R8Out;
+;   UINT64    R9Out;
+;   UINT8     *CallPending;
+; } SVSM_CALL_DATA;
+;
+; UINT32
+; EFIAPI
+; AsmVmgExitSvsm (
+;   SVSM_CALL_DATA *SvsmCallData
+;   );
+;------------------------------------------------------------------------------
+global ASM_PFX(AsmVmgExitSvsm)
+ASM_PFX(AsmVmgExitSvsm):
+    push    r10
+    push    r11
+    push    r12
+
+;
+; Calling convention has SvsmCallData in RCX. Move RCX to R12 in order to
+; properly populate the SVSM register state.
+;
+    mov     r12, rcx
+
+    mov     rax, [r12 + 8]
+    mov     rcx, [r12 + 16]
+    mov     rdx, [r12 + 24]
+    mov     r8,  [r12 + 32]
+    mov     r9,  [r12 + 40]
+
+;
+; Set CA call pending
+;
+    mov     r10, [r12]
+    mov     byte [r10], 1
+
+    rep     vmmcall
+
+    mov     [r12 + 48], rax
+    mov     [r12 + 56], rcx
+    mov     [r12 + 64], rdx
+    mov     [r12 + 72], r8
+    mov     [r12 + 80], r9
+
+;
+; Perform the atomic exchange and return the CA call pending value.
+; The call pending value is a one-byte field at offset 0 into the CA,
+; which is currently the value in R10.
+;
+
+    mov     r11, [r12 + 88]     ; Get CallPending address
+    mov     cl, byte [r11]
+    xchg    byte [r10], cl
+    mov     byte [r11], cl      ; Return the exchanged value
+
+    pop     r12
+    pop     r11
+    pop     r10
+
+;
+; RAX has the value to be returned from the SVSM
+;
+    ret
+