[PATCH] ARM: spectre-v2: fix smp_processor_id() warning

[Tetsuo Handa]

syzbot complains smp_processor_id() from harden_branch_predictor()
 from page fault path [1]. Explicitly disable preemption and use
raw_smp_processor_id().

Link: https://syzkaller.appspot.com/bug?extid=a7ee43e564223f195c84 [1]
Reported-by: syzbot <syzbot+a7ee43e564223f195c84@xxxxxxxxxxxxxxxxxxxxxxxxx>
Fixes: f5fe12b1eaee220c ("ARM: spectre-v2: harden user aborts in kernel space")
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
This patch is completely untested.

 arch/arm/include/asm/system_misc.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/system_misc.h b/arch/arm/include/asm/system_misc.h
index 98b37340376b..a92446769acd 100644
--- a/arch/arm/include/asm/system_misc.h
+++ b/arch/arm/include/asm/system_misc.h
@@ -20,8 +20,11 @@ typedef void (*harden_branch_predictor_fn_t)(void);
 DECLARE_PER_CPU(harden_branch_predictor_fn_t, harden_branch_predictor_fn);
 static inline void harden_branch_predictor(void)
 {
-	harden_branch_predictor_fn_t fn = per_cpu(harden_branch_predictor_fn,
-						  smp_processor_id());
+	harden_branch_predictor_fn_t fn;
+
+	preempt_disable_notrace();
+	fn = per_cpu(harden_branch_predictor_fn, raw_smp_processor_id());
+	preempt_enable_no_resched_notrace();
 	if (fn)
 		fn();
 }
-- 
2.18.4