subpage_prot in powerpc/mm from ubuntu_kernel_selftests failed

This issue was spotted on Bionic Power9 (passed on Power8)

$ sudo ./subpage_prot
test: subpage_prot_anon
tags: git_version:c186097-dirty
allocated malloc block of 0x4000000 bytes at 0x7cb0c1f00000
testing malloc block...
Failed at 0x7cb0c1f01000 (p=0,sp=1,w=1), want=fault, got=pass !
Failed at 0x7cb0c1f03000 (p=0,sp=3,w=0), want=fault, got=pass !
Failed at 0x7cb0c1f03000 (p=0,sp=3,w=1), want=fault, got=pass !
Failed at 0x7cb0c1f12000 (p=1,sp=2,w=1), want=fault, got=pass !
Failed at 0x7cb0c1f14000 (p=1,sp=4,w=0), want=fault, got=pass !

On Cosmic this test will be skipped on Power9

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: linux-image-4.15.0-44-generic 4.15.0-44.47
ProcVersionSignature: Ubuntu 4.15.0-44.47-generic 4.15.18
Uname: Linux 4.15.0-44-generic ppc64le
AlsaDevices:
 total 0
 crw-rw---- 1 root audio 116, 1 Jan 24 07:22 seq
 crw-rw---- 1 root audio 116, 33 Jan 24 07:22 timer
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay': 'aplay'
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: ppc64el
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord': 'arecord'
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
Date: Thu Jan 24 09:40:59 2019
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig': 'iwconfig'
Lsusb:
 Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
 Bus 001 Device 003: ID 0451:80ff Texas Instruments, Inc.
 Bus 001 Device 004: ID 0557:2419 ATEN International Co., Ltd
 Bus 001 Device 002: ID 0557:7000 ATEN International Co., Ltd Hub
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
PciMultimedia:

ProcFB: 0 astdrmfb
ProcKernelCmdLine: root=UUID=acd1a0d7-f6fc-4130-928c-c8b11ad6e4be ro console=hvc0
ProcLoadAvg: 0.07 0.29 0.49 1/1361 35602
ProcLocks:
 1: FLOCK ADVISORY WRITE 3482 00:17:520 0 EOF
 2: POSIX ADVISORY WRITE 3746 00:17:580 0 EOF
 3: POSIX ADVISORY WRITE 1800 00:17:368 0 EOF
 4: FLOCK ADVISORY WRITE 3744 00:17:568 0 EOF
 5: POSIX ADVISORY WRITE 3831 00:17:588 0 EOF
ProcSwaps:
 Filename Type Size Used Priority
 /swap.img file 8388544 0 -2
ProcVersion: Linux version 4.15.0-44-generic (buildd@bos02-ppc64el-004) (gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3)) #47-Ubuntu SMP Mon Jan 14 11:26:40 UTC 2019
RelatedPackageVersions:
 linux-restricted-modules-4.15.0-44-generic N/A
 linux-backports-modules-4.15.0-44-generic N/A
 linux-firmware 1.173.3
RfKill: Error: [Errno 2] No such file or directory: 'rfkill': 'rfkill'
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
VarLogDump_list: total 0
cpu_cores: Number of cores present = 40
cpu_coreson: Number of cores online = 40
cpu_dscr: DSCR is 4
cpu_freq:
 min: 2.862 GHz (cpu 159)
 max: 2.863 GHz (cpu 1)
 avg: 2.862 GHz
cpu_runmode:
 Could not retrieve current diagnostics mode,
 No kernel interface to firmware
cpu_smt: SMT=4