[RFC PATCH v2 2/3] getcpu_cache: wire up ARM system call

Wire up the getcpu cache system call on 32-bit ARM. Call the
getcpu_cache_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.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Russell King <redacted>
CC: Catalin Marinas <catalin.marinas@arm.com>
CC: Will Deacon <redacted>
CC: Thomas Gleixner <redacted>
CC: Paul Turner <redacted>
CC: Andrew Hunter <redacted>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Andi Kleen <redacted>
CC: Dave Watson <redacted>
CC: Chris Lameter <redacted>
CC: Ingo Molnar <mingo@redhat.com>
CC: Ben Maurer <redacted>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: "Paul E. McKenney" <redacted>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Thomas Gleixner <redacted>
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           | 1 +
 3 files changed, 3 insertions(+)

diff --git a/arch/arm/include/uapi/asm/unistd.h b/arch/arm/include/uapi/asm/unistd.h
index ede692f..ea0ea94 100644
--- a/arch/arm/include/uapi/asm/unistd.h
+++ b/arch/arm/include/uapi/asm/unistd.h

@@ -417,6 +417,7 @@
 #define __NR_userfaultfd		(__NR_SYSCALL_BASE+388)
 #define __NR_membarrier			(__NR_SYSCALL_BASE+389)
 #define __NR_mlock2			(__NR_SYSCALL_BASE+390)
+#define __NR_getcpu_cache		(__NR_SYSCALL_BASE+391)
 
 /*
  * The following SWIs are ARM private.

diff --git a/arch/arm/kernel/calls.S b/arch/arm/kernel/calls.S
index ac368bb..aa43e29 100644
--- a/arch/arm/kernel/calls.S
+++ b/arch/arm/kernel/calls.S

@@ -400,6 +400,7 @@
 		CALL(sys_userfaultfd)
 		CALL(sys_membarrier)
 		CALL(sys_mlock2)
+/* 391 */	CALL(sys_getcpu_cache)
 #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..ff5052c 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c

@@ -594,6 +594,7 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 			} else {
 				clear_thread_flag(TIF_NOTIFY_RESUME);
 				tracehook_notify_resume(regs);
+				getcpu_cache_handle_notify_resume(current);
 			}
 		}
 		local_irq_disable();

-- 
2.1.4