[SuperSU] m45k:
I tried flashing 2.82 stable, SR3, SR5 and 2.79 to my Xiaomi Mi8 with TWRP 3.2.2

i am always getting

- Patching sepolicy

--- Failure, aborting

Here my log file

*****************
SuperSU installer
*****************
- Mounting /system, /data and rootfs
mount: mounting /dev/block/sda21 on /data failed: Device or resource busy
2+0 records in
2+0 records out
2 bytes (2B) copied, 0.004740 seconds, 421B/s
3+0 records in
3+0 records out
3 bytes (3B) copied, 0.000742 seconds, 3.9KB/s
10+0 records in
10+0 records out
10 bytes (10B) copied, 0.001519 seconds, 6.4KB/s
0+0 records in
0+0 records out
0 bytes (0B) copied, 0.003365 seconds, 0B/s
/tmp/updater: line 989: /system/toolbox: not found
- Extracting files
Archive: /sdcard/TWRP/SuperSU-v2.82-201705271822.zip
inflating: META-INF/MANIFEST.MF
...
inflating: x86/supolicy
supolicy v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

Patching policy ...
-permissive:adbd_socket=ok
...
everything ok
...
-permissive:pdx_display_client_endpoint_dir_type=ok
- Success
- Detecting system compatibility
sukernel v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

Loading from [/dev/block/sde45] ...

magic: [ANDROID!]
kernel: [44394304] (44396544) @ 0x00008000
ramdisk: [1196884] (1200128) @ 0x01000000
second: [0] (0) @ 0x00f00000
tags: @ 0x00000100
page size: 4096
unused: [0x00000000] [0x10040126]
dtb(?): [0] (0)
name: []
command line: [console=ttyMSM0,115200n8 earlycon=msm_geni_serial,0xA84000 androidboot.hardware=qcom androidboot.console=ttyMSM0 video=vfb:640x400,bpp=32,memsize=3072000 msm_rtb.filter=0x237 ehci-hcd.park=3 lpm_levels.sleep_disabled=1 service_locator.enable=1 swiotlb=2048 androidboot.configfs=true androidboot.usbcontroller=a600000.dwc3 buildvariant=user androidboot.verifiedbootstate=green androidboot.selinux=permissive]
extra command line: []
id: [0xf280411076e4b6a906030ffc03c9777c254471e6000000000000000000000000]

Saving to [/sutmp/ramdisk.packed] ...

sukernel v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

Loading from [/sutmp/ramdisk.packed] ...

Decompressing [1196884] --> [3163136]

Saving to [/sutmp/ramdisk] ...

sukernel v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

Loading from [/sutmp/ramdisk] ...

----- patch check -----

Loading from cpio:[init.rc] ...

Finding [daemonsu]
-!Found

Finding [SuperSU:PATCH]
-!Found

Result: not patched

sukernel v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

Loading from [/sutmp/ramdisk] ...

Saving to [/sutmp/init] ...

sukernel v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

Loading from [/sutmp/ramdisk] ...

Saving to [/sutmp/init.rc] ...

sukernel v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

Loading from [/sutmp/ramdisk] ...

Could not locate entry
- System-less mode, boot image support required
- Creating image
Creating filesystem with parameters:
Size: 100663296
Block size: 4096
Blocks per group: 32768
Inodes per group: 6144
Inode size: 256
Journal blocks: 1024
Label:
Blocks: 24576
Block groups: 1
Reserved block group size: 7
Created filesystem with 11/6144 inodes and 1422/24576 blocks
/data/su.img: 11/6144 files (0.0% non-contiguous), 1422/24576 blocks
- Mounting image
I:Found no matching fstab entry for uevent device '/devices/virtual/block/loop0' - change
- Creating paths
- Removing old files
- Placing files
rm: can't remove '/su/bin/su': No such file or directory
rm: can't remove '/su/bin/daemonsu': No such file or directory
rm: can't remove '/su/bin/supolicy_wrapped': No such file or directory
rm: can't remove '/su/lib/libsupol.so': No such file or directory
rm: can't remove '/su/bin/sukernel': No such file or directory
rm: can't remove '/data/SuperSU.apk': No such file or directory

******************
Boot image patcher
******************
- Finding boot image
--- Boot image: /dev/block/sde45
sukernel v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

Loading from [/dev/block/sde45] ...

magic: [ANDROID!]
kernel: [44394304] (44396544) @ 0x00008000
ramdisk: [1196884] (1200128) @ 0x01000000
second: [0] (0) @ 0x00f00000
tags: @ 0x00000100
page size: 4096
unused: [0x00000000] [0x10040126]
dtb(?): [0] (0)
name: []
command line: [console=ttyMSM0,115200n8 earlycon=msm_geni_serial,0xA84000 androidboot.hardware=qcom androidboot.console=ttyMSM0 video=vfb:640x400,bpp=32,memsize=3072000 msm_rtb.filter=0x237 ehci-hcd.park=3 lpm_levels.sleep_disabled=1 service_locator.enable=1 swiotlb=2048 androidboot.configfs=true androidboot.usbcontroller=a600000.dwc3 buildvariant=user androidboot.verifiedbootstate=green androidboot.selinux=permissive]
extra command line: []
id: [0xf280411076e4b6a906030ffc03c9777c254471e6000000000000000000000000]

- Extracting ramdisk
sukernel v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

Loading from [/dev/block/sde45] ...

magic: [ANDROID!]
kernel: [44394304] (44396544) @ 0x00008000
ramdisk: [1196884] (1200128) @ 0x01000000
second: [0] (0) @ 0x00f00000
tags: @ 0x00000100
page size: 4096
unused: [0x00000000] [0x10040126]
dtb(?): [0] (0)
name: []
command line: [console=ttyMSM0,115200n8 earlycon=msm_geni_serial,0xA84000 androidboot.hardware=qcom androidboot.console=ttyMSM0 video=vfb:640x400,bpp=32,memsize=3072000 msm_rtb.filter=0x237 ehci-hcd.park=3 lpm_levels.sleep_disabled=1 service_locator.enable=1 swiotlb=2048 androidboot.configfs=true androidboot.usbcontroller=a600000.dwc3 buildvariant=user androidboot.verifiedbootstate=green androidboot.selinux=permissive]
extra command line: []
id: [0xf280411076e4b6a906030ffc03c9777c254471e6000000000000000000000000]

Saving to [/sutmp/ramdisk.packed] ...

- Decompressing ramdisk
sukernel v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

Loading from [/sutmp/ramdisk.packed] ...

Decompressing [1196884] --> [3163136]

Saving to [/sutmp/ramdisk] ...

- Checking patch status
sukernel v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

Loading from [/sutmp/ramdisk] ...

----- patch check -----

Loading from cpio:[init.rc] ...

Finding [daemonsu]
-!Found

Finding [SuperSU:PATCH]
-!Found

Result: not patched

- Creating backup
rm: can't remove '/data/stock_boot_*.img': No such file or directory
rm: can't remove '/data/stock_boot_*.img.gz': No such file or directory
rm: can't remove '/cache/stock_boot_*.img': No such file or directory
rm: can't remove '/cache/stock_boot_*.img.gz': No such file or directory
sukernel v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

[/dev/block/sde45](67108864) --> [/data/stock_boot_75488b4aa1d0c08be3809aaf360da7362a484d3b.img.gz](19841190)

rm: can't remove '/sutmp/ramdisk.original': No such file or directory
- Patching sepolicy
sukernel v2.82 (ndk:arm64-v8a) - Copyright (C) 2014-2017 - Chainfire & CCMT

Loading from [/sutmp/ramdisk] ...

Could not locate entry
--- Failure, aborting

*************************
IMPORTANT NOTICES
*************************
I:Found no matching fstab entry for uevent device '/devices/virtual/block/loop0' - change
First reboot may take a
few minutes. It can also
loop a few times. Do not
interrupt the process!
*************************

- Unmounting /system
- Done !

can anybody give me an advice on how to manage to get SuperSU installed?