x86/realmode: Remove trampoline_status

There is no reader of trampoline_status, it's only written.

It turns out that after commit ce4b1b1 ("x86/smpboot: Initialize
secondary CPU only if master CPU will wait for it"), trampoline_status is
not needed any more.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/1563266424-3472-1-git-send-email-kernelfans@gmail.com

Author: liupingfan

arch/x86/include/asm/realmode.h

@@ -20,7 +20,6 @@ struct real_mode_header {
 	u32	ro_end;
 	/* SMP trampoline */
 	u32	trampoline_start;
-	u32	trampoline_status;
 	u32	trampoline_header;
 #ifdef CONFIG_X86_64
 	u32	trampoline_pgd;

arch/x86/kernel/smpboot.c

@@ -1023,8 +1023,6 @@ int common_cpu_up(unsigned int cpu, struct task_struct *idle)
 static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle,
 		       int *cpu0_nmi_registered)
 {
-	volatile u32 *trampoline_status =
-		(volatile u32 *) __va(real_mode_header->trampoline_status);
 	/* start_ip had better be page-aligned! */
 	unsigned long start_ip = real_mode_header->trampoline_start;
 
@@ -1116,9 +1114,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle,
 		}
 	}
 
-	/* mark "stuck" area as not stuck */
-	*trampoline_status = 0;
-
 	if (x86_platform.legacy.warm_reset) {
 		/*
 		 * Cleanup possible dangling ends...

arch/x86/realmode/rm/header.S

@@ -19,7 +19,6 @@ GLOBAL(real_mode_header)
 	.long	pa_ro_end
 	/* SMP trampoline */
 	.long	pa_trampoline_start
-	.long	pa_trampoline_status
 	.long	pa_trampoline_header
 #ifdef CONFIG_X86_64
 	.long	pa_trampoline_pgd;

arch/x86/realmode/rm/trampoline_32.S

@@ -41,9 +41,6 @@ ENTRY(trampoline_start)
 
 	movl	tr_start, %eax	# where we need to go
 
-	movl	$0xA5A5A5A5, trampoline_status
-				# write marker for master knows we're running
-
 	/*
 	 * GDT tables in non default location kernel can be beyond 16MB and
 	 * lgdt will not be able to load the address as in real mode default

arch/x86/realmode/rm/trampoline_64.S

@@ -49,9 +49,6 @@ ENTRY(trampoline_start)
 	mov	%ax, %es
 	mov	%ax, %ss
 
-	movl	$0xA5A5A5A5, trampoline_status
-	# write marker for master knows we're running
-
 	# Setup stack
 	movl	$rm_stack_end, %esp
 

arch/x86/realmode/rm/trampoline_common.S

@@ -2,7 +2,3 @@
 	.section ".rodata","a"
 	.balign	16
 tr_idt: .fill 1, 6, 0
-
-	.bss
-	.balign	4
-GLOBAL(trampoline_status)	.space	4