x86: add %gs accessors for x86_32

Impact: cleanup

On x86_32, %gs is handled lazily.  It's not saved and restored on
kernel entry/exit but only when necessary which usually is during task
switch but there are few other places.  Currently, it's done by
calling savesegment() and loadsegment() explicitly.  Define
get_user_gs(), set_user_gs() and task_user_gs() and use them instead.

While at it, clean up register access macros in signal.c.

This cleans up code a bit and will help future changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 6 insertions, 8 deletions

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 0a5df5f82fb9..508b6b57d0c3 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -90,9 +90,10 @@ static u16 get_segment_reg(struct task_struct *task, unsigned long offset)
         if (offset != offsetof(struct user_regs_struct, gs))
                 retval = *pt_regs_access(task_pt_regs(task), offset);
         else {
-                retval = task->thread.gs;
                 if (task == current)
-                        savesegment(gs, retval);
+                        retval = get_user_gs(task_pt_regs(task));
+                else
+                        retval = task_user_gs(task);
         }
         return retval;
 }
@@ -126,13 +127,10 @@ static int set_segment_reg(struct task_struct *task,
                 break;
 
         case offsetof(struct user_regs_struct, gs):
-                task->thread.gs = value;
                 if (task == current)
-                        /*
-                         * The user-mode %gs is not affected by
-                         * kernel entry, so we must update the CPU.
-                         */
-                        loadsegment(gs, value);
+                        set_user_gs(task_pt_regs(task), value);
+                else
+                        task_user_gs(task) = value;
         }
 
         return 0;