[Bug 201753] AMD-Vi: Unable to write to IOMMU perf counter

bugzilla-daemon
2021-03-16T11:15:25Z

--- Comment #23 from David Coe (david.coe@live.co.uk) ---
I would guess that the difference between warm and cold boot is due to your
Ryzen 2500U (like my 2440G) hovering between needing 5 and 6 tries of 20 msecs.
Without adding Paul's logging you can't tell!

If it would help anyone (and you trust a non-official kernel recompile) I have
placed 4 variants on my Box account. Both Suravee's original patch with 25 x 20
msec tries maximum and logged and Alex's very simple patch are applied to
Ubuntu's 5.8.0-44 (20.10) and 5.10.0-14 (21.04) kernels.

The version numbers are identical so that Ubuntu's own DEB's for linux-tools,
linux-headers and linux-libc-dev are compatible. My linux-image replaces their
own linux-image and linux-modules so take care that you can still boot from a
'known' kernel.

They all work for me with quite heavy use on KVM but YMMV :-). Mail me if you
need access.

Best regards to all and my thanks to Suravee, Alex and Paul!

David