[RFC PATCH v2 3/3] thread_local_abi: wire up ARM system call

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

Wire up the thread local ABI on ARM32. Call the
thread_local_abi_handle_notify_resume() function on return to
userspace if TIF_NOTIFY_RESUME thread flag is set.

This provides an ABI improving the speed of a getcpu operation
on ARM by skipping the getcpu system call on the fast path.

[ Untested. ]

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Russell King <linux@arm.linux.org.uk>
CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Will Deacon <will.deacon@arm.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Paul Turner <pjt@google.com>
CC: Andrew Hunter <ahh@google.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Andi Kleen <andi@firstfloor.org>
CC: Dave Watson <davejwatson@fb.com>
CC: Chris Lameter <cl@linux.com>
CC: Ingo Molnar <mingo@redhat.com>
CC: Ben Maurer <bmaurer@fb.com>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: linux-api@vger.kernel.org
---
 arch/arm/include/uapi/asm/unistd.h | 1 +
 arch/arm/kernel/calls.S            | 1 +
 arch/arm/kernel/signal.c           | 2 ++
 3 files changed, 4 insertions(+)

diff --git a/arch/arm/include/uapi/asm/unistd.h b/arch/arm/include/uapi/asm/unistd.h
index 7a2a32a..859433a 100644
--- a/arch/arm/include/uapi/asm/unistd.h
+++ b/arch/arm/include/uapi/asm/unistd.h
@@ -416,6 +416,7 @@
 #define __NR_execveat			(__NR_SYSCALL_BASE+387)
 #define __NR_userfaultfd		(__NR_SYSCALL_BASE+388)
 #define __NR_membarrier			(__NR_SYSCALL_BASE+389)
+#define __NR_thread_local_abi		(__NR_SYSCALL_BASE+390)
 
 /*
  * The following SWIs are ARM private.
diff --git a/arch/arm/kernel/calls.S b/arch/arm/kernel/calls.S
index fde6c88..82b59cc 100644
--- a/arch/arm/kernel/calls.S
+++ b/arch/arm/kernel/calls.S
@@ -399,6 +399,7 @@
 		CALL(sys_execveat)
 		CALL(sys_userfaultfd)
 		CALL(sys_membarrier)
+/* 390 */	CALL(sys_thread_local_abi)
 #ifndef syscalls_counted
 .equ syscalls_padding, ((NR_syscalls + 3) & ~3) - NR_syscalls
 #define syscalls_counted
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 7b8f214..c64cd2f 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -594,6 +594,8 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 			} else {
 				clear_thread_flag(TIF_NOTIFY_RESUME);
 				tracehook_notify_resume(regs);
+				if (thread_local_abi_active(current))
+					thread_local_abi_handle_notify_resume(current);
 			}
 		}
 		local_irq_disable();
-- 
2.1.4