x86/asm/entry/64: Get rid of the FIXUP_TOP_OF_STACK/RESTORE_TOP_OF_STACK macros

x86/asm/entry/64: Get rid of the FIXUP_TOP_OF_STACK/RESTORE_TOP_OF_STACK macros

The FIXUP_TOP_OF_STACK macro is only necessary because we don't save %r11
to pt_regs->r11 on SYSCALL64 fast path, but we want ptrace to see it populated.

Bite the bullet, add a single additional PUSH instruction, and remove
the FIXUP_TOP_OF_STACK macro.

The RESTORE_TOP_OF_STACK macro is already a nop. Remove it too.

On SandyBridge CPU, it does not get slower:
measured 54.22 ns per getpid syscall before and after last two
changes on defconfig kernel.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
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/1426785469-15125-4-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>