I'm running an AMD Ryzen Threadripper 1920X CPU on a MSI X399 Gaming PRO Carbon board on Linux (Debian unstable, Linux kernel 4.17.17-1 from Debian)
After the upgrade to the latest available MSI BIOS which includes the AGESA Code 1.1.01A I ran into different problems on a linux system (udev timeout, kvm module does not load).
As from other bugreports  this problem seems not related to MSI, so it looks like an issue in the AGESA code.
The source of the issue seems to be that the CPU/BIOS advertises SEV support even if it does not.
According to the AMD docs , the EAX register in 0x8000001f holds the information about the support for SME (bit 0), SEV (bit 1), VmPageFlush (bit 2) and SevEs (bit 3).
With the command 'x86info -r | grep 0x8000001f' I see the content of the EAX register is set to 0x7. Which I read as support for SME, SEV and VmPageFlush.
But apperantly AMD Threadripper family does not support SEV.
Additionally what I read the requirement comes from AGESA (please confirm): It is currently officially not possible to downgrade BIOSes running newer AGESA codes, which means that if a new BIOS update breaks something, the user is stuck until a new BIOS update fixing the issue is released.
Kind Regards Michael Musenbrock
PS: I already forwarded the issue to MSI, but as I did not find the report either on a MSI nor on a official AMD site, I wanted to add it to the support forum
 Open-Source Register Reference For AMD Family 17h Processors Models 00h-2Fh: https://developer.amd.com/wp-content/resources/56255_3_03.PDF