stage1: support TDX in trampoline-only mode

Since TDP is the only platform right now that uses stage1-trampoline,
only allow platform type TDP when in trampoline-only mode. All TD vCPUs
start execution in 32-bit mode concurrently and therefore only TD BSP is
allowed to use the stage2 stack. Program an invalid address (0x7ffff000)
into a TD AP's ESP register. This address is chosen because a) it is
usually not an MMIO address and b) it is an unaccepted page if it's
backed by memory.

Signed-off-by: Peter Fang <[email protected]>

stage1/stage1.S

@@ -41,9 +41,7 @@ startup_32:
 2:	popl	%ebp
 	leal	2b, %eax
 	subl	%eax, %ebp
-#endif
 
-#ifdef LOAD_STAGE2
 	leal	stage2_bin(%ebp), %esi
 	movl	$STAGE2_START, %edi
 	movl	stage2_size(%ebp), %ecx
@@ -75,14 +73,35 @@ startup_32:
 	/* Reserve space for VTOM */
 	pushl	%eax
 	pushl	%eax
-
 #else
-	/* Setup stack for stage 2 */
+	/*
+	 * Stage 2 launch info has been prepared
+	 * Make sure platform type is TDP
+	 */
+	movl	$(STAGE2_START - 24), %eax
+	movl	(%eax), %eax
+	cmpl	$2, %eax
+	je	.Lsetup_td
+	ud2
+
+.Lsetup_td:
+	/* %esi is initialized with TD CPU index */
+	test	%esi, %esi
+	jz	.Lsetup_bsp_stack
+
+	/* Set up invalid stack for APs since they must run stacklessly */
+	movl	$0x7ffff000, %esp
+	jmp	.Lenter_stage2
+.Lsetup_bsp_stack:
+	/* Set up BSP stack for stage 2 */
 	movl	$(STAGE2_START - 32), %esp
+.Lenter_stage2:
 #endif
+
 	/* Jump to stage 2 */
 	movl	$STAGE2_START, %eax
 	jmp	*%eax
+
 .data
 
 #ifdef LOAD_STAGE2