From: Martin Schwidefsky <schwidefsky@de.ibm.com>
Date: Fri, 31 Aug 2018 10:42:24 +0200
Subject: init: add arch_call_rest_init to allow stack switching
Git-commit: 53c99bd665a2649341ed6aed358ab56a3eedcd00
Patch-mainline: v4.20-rc1
References: jsc#SLE-11178

With CONFIG_VMAP_STACK=y the kernel stack of all tasks should be
allocated in the vmalloc space. The initial stack used for all
the early init code is in the init_thread_union. To be able to
switch from this early stack to a properly allocated stack
from vmalloc the architecture needs a switch-over point.

Introduce the arch_call_rest_init() function with a weak definition
in init/main.c with the only purpose to call rest_init() from the
end of start_kernel(). The architecture override can then do the
necessary magic to switch to the new vmalloc'ed stack.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
---
 include/linux/start_kernel.h |    2 ++
 init/main.c                  |    9 +++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

--- a/include/linux/start_kernel.h
+++ b/include/linux/start_kernel.h
@@ -8,5 +8,7 @@
    up something else. */
 
 extern asmlinkage void __init start_kernel(void);
+extern void __init arch_call_rest_init(void);
+extern void __ref rest_init(void);
 
 #endif /* _LINUX_START_KERNEL_H */
--- a/init/main.c
+++ b/init/main.c
@@ -388,7 +388,7 @@ static void __init setup_command_line(ch
 
 static __initdata DECLARE_COMPLETION(kthreadd_done);
 
-static noinline void __ref rest_init(void)
+noinline void __ref rest_init(void)
 {
 	int pid;
 
@@ -492,6 +492,11 @@ static void __init mm_init(void)
 	pti_init();
 }
 
+void __init __weak arch_call_rest_init(void)
+{
+	rest_init();
+}
+
 asmlinkage __visible void __init start_kernel(void)
 {
 	char *command_line;
@@ -688,7 +693,7 @@ asmlinkage __visible void __init start_k
 	}
 
 	/* Do the rest non-__init'ed, we're now alive */
-	rest_init();
+	arch_call_rest_init();
 }
 
 /* Call all constructor functions linked into the kernel. */