x86/asm: Remove thread_info.sysenter_return

It's no longer needed.

We could reinstate something like it as an optimization, which
would remove two cachelines from the fast syscall entry working
set.  I benchmarked it, and it makes no difference whatsoever to
the performance of cache-hot compat syscalls on Sandy Bridge.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/f08cc0cff30201afe9bb565c47134c0a6c1a96a2.1444091585.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/thread_info.h

@@ -59,7 +59,6 @@ struct thread_info {
 	__u32			cpu;		/* current CPU */
 	int			saved_preempt_count;
 	mm_segment_t		addr_limit;
-	void __user		*sysenter_return;
 	unsigned int		sig_on_uaccess_error:1;
 	unsigned int		uaccess_err:1;	/* uaccess failed */
 };

arch/x86/kernel/asm-offsets.c

@@ -53,9 +53,6 @@ void common(void) {
 	OFFSET(IA32_SIGCONTEXT_sp, sigcontext_ia32, sp);
 	OFFSET(IA32_SIGCONTEXT_ip, sigcontext_ia32, ip);
 
-	BLANK();
-	OFFSET(TI_sysenter_return, thread_info, sysenter_return);
-
 	BLANK();
 	OFFSET(IA32_RT_SIGFRAME_sigcontext, rt_sigframe_ia32, uc.uc_mcontext);
 #endif