AMD has known about this since August of last year, and hasn't responded. Given how Zen 3 is supposed to be a completely new design, not a revision of Zen 2, and given this was disclosed to AMD last year, it's quite possible it will be hardware mitigated, but that's of little comfort to all the people who bought Zen 2 based EPYCs...
https://www.tomshardware.com/news/new-amd-side-channel-attacks-discovered-impacts-zen-architecture
