[RFC PATCH 2/2] thread_local_abi: wire up ARM system call

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

This provides a way to implement a sched_getcpu() on ARM without
requiring to perform a system call on the fast path.

[ Untested. ]

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org>
CC: Russell King <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>
CC: Catalin Marinas <redacted>
CC: Will Deacon <redacted>
CC: Thomas Gleixner <redacted>
CC: Paul Turner <redacted>
CC: Andrew Hunter <redacted>
CC: Peter Zijlstra <redacted>
CC: Andy Lutomirski <redacted>
CC: Andi Kleen <andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org>
CC: Dave Watson <redacted>
CC: Chris Lameter <redacted>
CC: Ingo Molnar <redacted>
CC: Ben Maurer <redacted>
CC: Steven Rostedt <redacted>
CC: "Paul E. McKenney" <redacted>
CC: Josh Triplett <redacted>
CC: Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
CC: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
CC: Thomas Gleixner <redacted>
CC: linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
---
 arch/arm/include/asm/unistd.h      | 2 +-
 arch/arm/include/uapi/asm/unistd.h | 1 +
 arch/arm/kernel/calls.S            | 1 +
 arch/arm/kernel/signal.c           | 2 ++
 4 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/unistd.h b/arch/arm/include/asm/unistd.h
index 7b84657..ef55382 100644
--- a/arch/arm/include/asm/unistd.h
+++ b/arch/arm/include/asm/unistd.h

@@ -19,7 +19,7 @@
  * This may need to be greater than __NR_last_syscall+1 in order to
  * account for the padding in the syscall table
  */
-#define __NR_syscalls  (392)
+#define __NR_syscalls  (393)
 
 #define __ARCH_WANT_STAT64
 #define __ARCH_WANT_SYS_GETHOSTNAME

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..feaa514 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 (getcpu_cache_active(current))
+					getcpu_cache_handle_notify_resume(current);
 			}
 		}
 		local_irq_disable();

-- 
2.1.4