[PATCH 2/3] x86: Unify and fix init sp0

[Andy Lutomirski <luto@amacapital.net>]

x86_32 and x86_64 need slightly different sp0 values, and x86_32's was
incorrect for init.  (This never mattered -- the init thread never
runs user code, so we never used sp0 for anything.)

Fix it and mostly unify them.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
---
 arch/x86/include/asm/processor.h | 7 +++++--
 arch/x86/kernel/process.c        | 2 +-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 88d9aa745898..fc6d8d0d8d53 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -811,6 +811,9 @@ static inline void spin_lock_prefetch(const void *x)
 	prefetchw(x);
 }
 
+#define TOP_OF_INIT_STACK ((unsigned long)&init_stack + sizeof(init_stack) - \
+			   TOP_OF_KERNEL_STACK_PADDING)
+
 #ifdef CONFIG_X86_32
 /*
  * User space process size: 3GB (default).
@@ -821,7 +824,7 @@ static inline void spin_lock_prefetch(const void *x)
 #define STACK_TOP_MAX		STACK_TOP
 
 #define INIT_THREAD  {							  \
-	.sp0			= sizeof(init_stack) + (long)&init_stack, \
+	.sp0			= TOP_OF_INIT_STACK,			  \
 	.vm86_info		= NULL,					  \
 	.sysenter_cs		= __KERNEL_CS,				  \
 	.io_bitmap_ptr		= NULL,					  \
@@ -883,7 +886,7 @@ extern unsigned long thread_saved_pc(struct task_struct *tsk);
 #define STACK_TOP_MAX		TASK_SIZE_MAX
 
 #define INIT_THREAD  { \
-	.sp0 = (unsigned long)&init_stack + sizeof(init_stack) \
+	.sp0 = TOP_OF_INIT_STACK \
 }
 
 /*
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index f4c0af7fc3a0..12b1cf606ddf 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -39,7 +39,7 @@
  */
 __visible DEFINE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss) = {
 	.x86_tss = {
-		.sp0 = (unsigned long)&init_stack + sizeof(init_stack),
+		.sp0 = TOP_OF_INIT_STACK,
 #ifdef CONFIG_X86_32
 		.ss0 = __KERNEL_DS,
 		.ss1 = __KERNEL_CS,
-- 
2.3.0