1 files changed, 154 insertions, 0 deletions
diff --git a/roms/edk2/OvmfPkg/CpuHotplugSmm/FirstSmiHandler.nasm b/roms/edk2/OvmfPkg/CpuHotplugSmm/FirstSmiHandler.nasm
new file mode 100644
index 000000000..5399b5fa4
--- /dev/null
+++ b/roms/edk2/OvmfPkg/CpuHotplugSmm/FirstSmiHandler.nasm
@@ -0,0 +1,154 @@
+;------------------------------------------------------------------------------
+; @file
+; Relocate the SMBASE on a hot-added CPU when it services its first SMI.
+;
+; Copyright (c) 2020, Red Hat, Inc.
+;
+; SPDX-License-Identifier: BSD-2-Clause-Patent
+;
+; The routine runs on the hot-added CPU in the following "big real mode",
+; 16-bit environment; per "SMI HANDLER EXECUTION ENVIRONMENT" in the Intel SDM
+; (table "Processor Register Initialization in SMM"):
+;
+;  - CS selector: 0x3000 (most significant 16 bits of SMM_DEFAULT_SMBASE).
+;
+;  - CS limit: 0xFFFF_FFFF.
+;
+;  - CS base: SMM_DEFAULT_SMBASE (0x3_0000).
+;
+;  - IP: SMM_HANDLER_OFFSET (0x8000).
+;
+;  - ES, SS, DS, FS, GS selectors: 0.
+;
+;  - ES, SS, DS, FS, GS limits: 0xFFFF_FFFF.
+;
+;  - ES, SS, DS, FS, GS bases: 0.
+;
+;  - Operand-size and address-size override prefixes can be used to access the
+;    address space beyond 1MB.
+;------------------------------------------------------------------------------
+
+SECTION .data
+BITS 16
+
+;
+; Bring in SMM_DEFAULT_SMBASE from
+; "MdePkg/Include/Register/Intel/SmramSaveStateMap.h".
+;
+SMM_DEFAULT_SMBASE: equ 0x3_0000
+
+;
+; Field offsets in FIRST_SMI_HANDLER_CONTEXT, which resides at
+; SMM_DEFAULT_SMBASE.
+;
+ApicIdGate:      equ  0 ; UINT64
+NewSmbase:       equ  8 ; UINT32
+AboutToLeaveSmm: equ 12 ; UINT8
+
+;
+; SMRAM Save State Map field offsets, per the AMD (not Intel) layout that QEMU
+; implements. Relative to SMM_DEFAULT_SMBASE.
+;
+SaveStateRevId:    equ 0xFEFC ; UINT32
+SaveStateSmbase:   equ 0xFEF8 ; UINT32
+SaveStateSmbase64: equ 0xFF00 ; UINT32
+
+;
+; CPUID constants, from "MdePkg/Include/Register/Intel/Cpuid.h".
+;
+CPUID_SIGNATURE:         equ 0x00
+CPUID_EXTENDED_TOPOLOGY: equ 0x0B
+CPUID_VERSION_INFO:      equ 0x01
+
+GLOBAL ASM_PFX (mFirstSmiHandler)     ; UINT8[]
+GLOBAL ASM_PFX (mFirstSmiHandlerSize) ; UINT16
+
+ASM_PFX (mFirstSmiHandler):
+  ;
+  ; Get our own APIC ID first, so we can contend for ApicIdGate.
+  ;
+  ; This basically reimplements GetInitialApicId() from
+  ; "UefiCpuPkg/Library/BaseXApicLib/BaseXApicLib.c".
+  ;
+  mov eax, CPUID_SIGNATURE
+  cpuid
+  cmp eax, CPUID_EXTENDED_TOPOLOGY
+  jb GetApicIdFromVersionInfo
+
+  mov eax, CPUID_EXTENDED_TOPOLOGY
+  mov ecx, 0
+  cpuid
+  test ebx, 0xFFFF
+  jz GetApicIdFromVersionInfo
+
+  ;
+  ; EDX has the APIC ID, save it to ESI.
+  ;
+  mov esi, edx
+  jmp KnockOnGate
+
+GetApicIdFromVersionInfo:
+  mov eax, CPUID_VERSION_INFO
+  cpuid
+  shr ebx, 24
+  ;
+  ; EBX has the APIC ID, save it to ESI.
+  ;
+  mov esi, ebx
+
+KnockOnGate:
+  ;
+  ; See if ApicIdGate shows our own APIC ID. If so, swap it to MAX_UINT64
+  ; (close the gate), and advance. Otherwise, keep knocking.
+  ;
+  ; InterlockedCompareExchange64():
+  ; - Value                   := &FIRST_SMI_HANDLER_CONTEXT.ApicIdGate
+  ; - CompareValue  (EDX:EAX) := APIC ID (from ESI)
+  ; - ExchangeValue (ECX:EBX) := MAX_UINT64
+  ;
+  mov edx, 0
+  mov eax, esi
+  mov ecx, 0xFFFF_FFFF
+  mov ebx, 0xFFFF_FFFF
+  lock cmpxchg8b [ds : dword (SMM_DEFAULT_SMBASE + ApicIdGate)]
+  jz ApicIdMatch
+  pause
+  jmp KnockOnGate
+
+ApicIdMatch:
+  ;
+  ; Update the SMBASE field in the SMRAM Save State Map.
+  ;
+  ; First, calculate the address of the SMBASE field, based on the SMM Revision
+  ; ID; store the result in EBX.
+  ;
+  mov eax, dword [ds : dword (SMM_DEFAULT_SMBASE + SaveStateRevId)]
+  test eax, 0xFFFF
+  jz LegacySaveStateMap
+
+  mov ebx, SMM_DEFAULT_SMBASE + SaveStateSmbase64
+  jmp UpdateSmbase
+
+LegacySaveStateMap:
+  mov ebx, SMM_DEFAULT_SMBASE + SaveStateSmbase
+
+UpdateSmbase:
+  ;
+  ; Load the new SMBASE value into EAX.
+  ;
+  mov eax, dword [ds : dword (SMM_DEFAULT_SMBASE + NewSmbase)]
+  ;
+  ; Save it to the SMBASE field whose address we calculated in EBX.
+  ;
+  mov dword [ds : dword ebx], eax
+  ;
+  ; Set AboutToLeaveSmm.
+  ;
+  mov byte [ds : dword (SMM_DEFAULT_SMBASE + AboutToLeaveSmm)], 1
+  ;
+  ; We're done; leave SMM and continue to the pen.
+  ;
+  rsm
+
+ASM_PFX (mFirstSmiHandlerSize):
+  dw $ - ASM_PFX (mFirstSmiHandler)