x86/asm/entry/64: Save user RSP in pt_regs->sp on SYSCALL64 fastpath

Prepare for the removal of 'usersp', by simplifying PER_CPU(old_rsp) usage:

  - use it only as temp storage

  - store the userspace stack pointer immediately in pt_regs->sp
    on syscall entry, instead of using it later, on syscall exit.

  - change C code to use pt_regs->sp only, instead of PER_CPU(old_rsp)
    and task->thread.usersp.

FIXUP/RESTORE_TOP_OF_STACK are simplified as well.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1425926364-9526-4-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 3 insertions, 7 deletions

diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
index 59c6c401f79f..acdee09228b3 100644
--- a/arch/x86/include/asm/compat.h
+++ b/arch/x86/include/asm/compat.h
@@ -301,7 +301,7 @@ static inline void __user *arch_compat_alloc_user_space(long len)
                 sp = task_pt_regs(current)->sp;
         } else {
                 /* -128 for the x32 ABI redzone */
-                sp = this_cpu_read(old_rsp) - 128;
+                sp = task_pt_regs(current)->sp - 128;
         }
 
         return (void __user *)round_down(sp - len, 16);
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 4077d963a1a0..74bb2e0f3030 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -145,12 +145,8 @@ static inline bool user_64bit_mode(struct pt_regs *regs)
 #endif
 }
 
-#define current_user_stack_pointer()    this_cpu_read(old_rsp)
-/* ia32 vs. x32 difference */
-#define compat_user_stack_pointer()     \
-        (test_thread_flag(TIF_IA32)     \
-         ? current_pt_regs()->sp        \
-         : this_cpu_read(old_rsp))
+#define current_user_stack_pointer()    current_pt_regs()->sp
+#define compat_user_stack_pointer()     current_pt_regs()->sp
 #endif
 
 #ifdef CONFIG_X86_32