[tip:x86/asm] x86/entry/32: Fix cpu_current_top_of_stack initialization at boot

[tip-bot for Andy Lutomirski]

Commit-ID:  cd493a6deb8b78eca280d05f7fa73fd69403ae29
Gitweb:     https://git.kernel.org/tip/cd493a6deb8b78eca280d05f7fa73fd69403ae29
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Thu, 2 Nov 2017 00:59:15 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 2 Nov 2017 11:04:47 +0100

x86/entry/32: Fix cpu_current_top_of_stack initialization at boot

cpu_current_top_of_stack's initialization forgot about
TOP_OF_KERNEL_STACK_PADDING.  This bug didn't matter because the
idle threads never enter user mode.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
Cc: Borislav Petkov <bpetkov@xxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/e5e370a7e6e4fddd1c4e4cf619765d96bb874b21.1509609304.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/smpboot.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index ad59edd..06c18fe 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -961,8 +961,7 @@ void common_cpu_up(unsigned int cpu, struct task_struct *idle)
 #ifdef CONFIG_X86_32
 	/* Stack for startup_32 can be just as for start_secondary onwards */
 	irq_ctx_init(cpu);
-	per_cpu(cpu_current_top_of_stack, cpu) =
-		(unsigned long)task_stack_page(idle) + THREAD_SIZE;
+	per_cpu(cpu_current_top_of_stack, cpu) = task_top_of_stack(idle);
 #else
 	initial_gs = per_cpu_offset(cpu);
 #endif