syzbot has bisected this bug to:

commit 83d116c53058d505ddef051e90ab27f57015b025
Author: Jia He [off-list ref]
Date:   Fri Oct 11 14:09:39 2019 +0000

     mm: fix double page fault on arm64 if PTE_AF is cleared

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1378f5b6e00000
start commit:   e31736d9 Merge tag 'nios2-v5.5-rc2' of git://git.kernel.or..
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=10f8f5b6e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1778f5b6e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=79f79de2a27d3e3d
dashboard link: https://syzkaller.appspot.com/bug?extid=9301f2f33873407d5b33
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10fd9fb1e00000

Reported-by: syzbot+9301f2f33873407d5b33@syzkaller.appspotmail.com
Fixes: 83d116c53058 ("mm: fix double page fault on arm64 if PTE_AF is  
cleared")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection