[tip:x86/asm] x86/entry: Remove TIF_SINGLESTEP entry work

[tip-bot for Andy Lutomirski <tipbot@zytor.com>]

Commit-ID:  392a62549fbb80da48811d04391615a25c39d091
Gitweb:     http://git.kernel.org/tip/392a62549fbb80da48811d04391615a25c39d091
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Wed, 9 Mar 2016 19:00:34 -0800
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 10 Mar 2016 09:48:14 +0100

x86/entry: Remove TIF_SINGLESTEP entry work

Now that SYSENTER with TF set puts X86_EFLAGS_TF directly into
regs->flags, we don't need a TIF_SINGLESTEP fixup in the syscall
entry code.  Remove it.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
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: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/2d15f24da52dafc9d2f0b8d76f55544f4779c517.1457578375.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/entry/common.c            | 10 ----------
 arch/x86/include/asm/thread_info.h |  2 +-
 2 files changed, 1 insertion(+), 11 deletions(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 1a000f5..209ba33 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -172,16 +172,6 @@ long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch,
 	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
 		BUG_ON(regs != task_pt_regs(current));
 
-	/*
-	 * If we stepped into a sysenter/syscall insn, it trapped in
-	 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
-	 * If user-mode had set TF itself, then it's still clear from
-	 * do_debug() and we need to set it again to restore the user
-	 * state.  If we entered on the slow path, TF was already set.
-	 */
-	if (work & _TIF_SINGLESTEP)
-		regs->flags |= X86_EFLAGS_TF;
-
 #ifdef CONFIG_SECCOMP
 	/*
 	 * Call seccomp_phase2 before running the other hooks so that
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index c0778fc..f2e2302 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -137,7 +137,7 @@ struct thread_info {
 /* work to do in syscall_trace_enter() */
 #define _TIF_WORK_SYSCALL_ENTRY	\
 	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU | _TIF_SYSCALL_AUDIT |	\
-	 _TIF_SECCOMP | _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT |	\
+	 _TIF_SECCOMP | _TIF_SYSCALL_TRACEPOINT |	\
 	 _TIF_NOHZ)
 
 /* work to do on any return to user space */