x86/entry/64: Remove all remaining direct thread_struct::sp0 reads

The only remaining readers in context switch code or vm86(), and
they all just want to update TSS.sp0 to match the current task.
Replace them all with a new helper update_sp0().

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/2d231687f4ff288c9d9e98d7861b7df374246ac3.1509609304.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

4 files changed, 10 insertions, 4 deletions

diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index 7ae8caffbada..54e64d909725 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -84,4 +84,10 @@ static inline void refresh_sysenter_cs(struct thread_struct *thread)
 }
 #endif
 
+/* This is used when switching tasks or entering/exiting vm86 mode. */
+static inline void update_sp0(struct task_struct *task)
+{
+        load_sp0(task->thread.sp0);
+}
+
 #endif /* _ASM_X86_SWITCH_TO_H */
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 40b85870e429..45bf0c5f93e1 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -287,7 +287,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
          * current_thread_info().  Refresh the SYSENTER configuration in
          * case prev or next is vm86.
          */
-        load_sp0(next->sp0);
+        update_sp0(next_p);
         refresh_sysenter_cs(next);
         this_cpu_write(cpu_current_top_of_stack,
                        (unsigned long)task_stack_page(next_p) +
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 2124304fb77a..45e380958392 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -465,7 +465,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
         this_cpu_write(current_task, next_p);
 
         /* Reload sp0. */
-        load_sp0(next->sp0);
+        update_sp0(next_p);
 
         /*
          * Now maybe reload the debug registers and handle I/O bitmaps
diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
index 0f1d92cd20ad..a7b44c75c642 100644
--- a/arch/x86/kernel/vm86_32.c
+++ b/arch/x86/kernel/vm86_32.c
@@ -148,7 +148,7 @@ void save_v86_state(struct kernel_vm86_regs *regs, int retval)
         preempt_disable();
         tsk->thread.sp0 = vm86->saved_sp0;
         tsk->thread.sysenter_cs = __KERNEL_CS;
-        load_sp0(tsk->thread.sp0);
+        update_sp0(tsk);
         refresh_sysenter_cs(&tsk->thread);
         vm86->saved_sp0 = 0;
         preempt_enable();
@@ -373,7 +373,7 @@ static long do_sys_vm86(struct vm86plus_struct __user *user_vm86, bool plus)
                 refresh_sysenter_cs(&tsk->thread);
         }
 
-        load_sp0(tsk->thread.sp0);
+        update_sp0(tsk);
         preempt_enable();
 
         if (vm86->flags & VM86_SCREEN_BITMAP)