[tip:x86/asm] x86/entry: Add task_top_of_stack() to find the top of a task's stack

[tip-bot for Andy Lutomirski]

Commit-ID:  3500130b84a3cdc5b6796eba1daf178944935efe
Gitweb:     https://git.kernel.org/tip/3500130b84a3cdc5b6796eba1daf178944935efe
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Thu, 2 Nov 2017 00:59:11 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 2 Nov 2017 11:04:44 +0100

x86/entry: Add task_top_of_stack() to find the top of a task's stack

This will let us get rid of a few places that hardcode accesses to
thread.sp0.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
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/b49b3f95a8ff858c40c9b0f5b32be0355324327d.1509609304.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/include/asm/processor.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 064b847..ad59cec 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -795,6 +795,8 @@ static inline void spin_lock_prefetch(const void *x)
 #define TOP_OF_INIT_STACK ((unsigned long)&init_stack + sizeof(init_stack) - \
 			   TOP_OF_KERNEL_STACK_PADDING)
 
+#define task_top_of_stack(task) ((unsigned long)(task_pt_regs(task) + 1))
+
 #ifdef CONFIG_X86_32
 /*
  * User space process size: 3GB (default).