Relevant: trail of bits posted a summary of this situation on their blog:
https://blog.trailofbits.com/2018/03/15/amd-flaws-technical-...
https://blog.trailofbits.com/2018/03/15/amd-flaws-technical-...
Possibly also relevant, previous HN discussion on another vulnerability on AMD's PSP, reported and fixed in December 2017 (but only disclosed in January 2018):