diff options
Diffstat (limited to 'UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm')
| -rw-r--r-- | UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm | 148 |
1 files changed, 148 insertions, 0 deletions
diff --git a/UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm b/UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm index 8bb1161fa0..7c2469f9c5 100644 --- a/UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm +++ b/UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm @@ -198,3 +198,151 @@ RestoreGhcb: SevEsGetApicIdExit:
OneTimeCallRet SevEsGetApicId
+
+
+;-------------------------------------------------------------------------------------
+;SwitchToRealProc procedure follows.
+;ALSO THIS PROCEDURE IS EXECUTED BY APs TRANSITIONING TO 16 BIT MODE. HENCE THIS PROC
+;IS IN MACHINE CODE.
+; SwitchToRealProc (UINTN BufferStart, UINT16 Code16, UINT16 Code32, UINTN StackStart)
+; rcx - Buffer Start
+; rdx - Code16 Selector Offset
+; r8 - Code32 Selector Offset
+; r9 - Stack Start
+;-------------------------------------------------------------------------------------
+SwitchToRealProcStart:
+BITS 64
+ cli
+
+ ;
+ ; Get RDX reset value before changing stacks since the
+ ; new stack won't be able to accomodate a #VC exception.
+ ;
+ push rax
+ push rbx
+ push rcx
+ push rdx
+
+ mov rax, 1
+ cpuid
+ mov rsi, rax ; Save off the reset value for RDX
+
+ pop rdx
+ pop rcx
+ pop rbx
+ pop rax
+
+ ;
+ ; Establish stack below 1MB
+ ;
+ mov rsp, r9
+
+ ;
+ ; Push ultimate Reset Vector onto the stack
+ ;
+ mov rax, rcx
+ shr rax, 4
+ push word 0x0002 ; RFLAGS
+ push ax ; CS
+ push word 0x0000 ; RIP
+ push word 0x0000 ; For alignment, will be discarded
+
+ ;
+ ; Get address of "16-bit operand size" label
+ ;
+ lea rbx, [PM16Mode]
+
+ ;
+ ; Push addresses used to change to compatibility mode
+ ;
+ lea rax, [CompatMode]
+ push r8
+ push rax
+
+ ;
+ ; Clear R8 - R15, for reset, before going into 32-bit mode
+ ;
+ xor r8, r8
+ xor r9, r9
+ xor r10, r10
+ xor r11, r11
+ xor r12, r12
+ xor r13, r13
+ xor r14, r14
+ xor r15, r15
+
+ ;
+ ; Far return into 32-bit mode
+ ;
+ retfq
+
+BITS 32
+CompatMode:
+ ;
+ ; Set up stack to prepare for exiting protected mode
+ ;
+ push edx ; Code16 CS
+ push ebx ; PM16Mode label address
+
+ ;
+ ; Disable paging
+ ;
+ mov eax, cr0 ; Read CR0
+ btr eax, 31 ; Set PG=0
+ mov cr0, eax ; Write CR0
+
+ ;
+ ; Disable long mode
+ ;
+ mov ecx, 0c0000080h ; EFER MSR number
+ rdmsr ; Read EFER
+ btr eax, 8 ; Set LME=0
+ wrmsr ; Write EFER
+
+ ;
+ ; Disable PAE
+ ;
+ mov eax, cr4 ; Read CR4
+ btr eax, 5 ; Set PAE=0
+ mov cr4, eax ; Write CR4
+
+ mov edx, esi ; Restore RDX reset value
+
+ ;
+ ; Switch to 16-bit operand size
+ ;
+ retf
+
+BITS 16
+ ;
+ ; At entry to this label
+ ; - RDX will have its reset value
+ ; - On the top of the stack
+ ; - Alignment data (two bytes) to be discarded
+ ; - IP for Real Mode (two bytes)
+ ; - CS for Real Mode (two bytes)
+ ;
+ ; This label is also used with AsmRelocateApLoop. During MP finalization,
+ ; the code from PM16Mode to SwitchToRealProcEnd is copied to the start of
+ ; the WakeupBuffer, allowing a parked AP to be booted by an OS.
+ ;
+PM16Mode:
+ mov eax, cr0 ; Read CR0
+ btr eax, 0 ; Set PE=0
+ mov cr0, eax ; Write CR0
+
+ pop ax ; Discard alignment data
+
+ ;
+ ; Clear registers (except RDX and RSP) before going into 16-bit mode
+ ;
+ xor eax, eax
+ xor ebx, ebx
+ xor ecx, ecx
+ xor esi, esi
+ xor edi, edi
+ xor ebp, ebp
+
+ iret
+
+SwitchToRealProcEnd:
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