I got my ThinkPad L14 this year (2020)
When I upgraded my Ubuntu from 20.04 to 20.10 I encountered blank screen.
In booting logs I saw this error:
AMD-Vi: Unable to read/write to IOMMU perf counter
and inspired by this Stackoverflow answer https://stackoverflow.com/questions/62827591/amd-vi-unable-to-read-write-to-iommu-coun-problem-loading-x-509-certificate/63112560
I did the following:
- in your GRUB boot menu select Advanced Ubuntu
- select your previous (working) kernel version, mine was 5.4
- log into Ubuntu
- edit GRUB
sudo vim /etc/default/grub
- change this line
GRUB_CMDLINE_LINUX="iommu=soft"and save the change
- restart and select your updated Ubuntu with kernel version 5.8
And it works!