AMD claims their processors aren't affected at all by any of the 3 variants of Foreshadow (https://www.amd.com/en/corporate/security-updates) therefore SMT is safe to leave enabled. On the other hand, on Intel the only fully comprehensive workaround is to completely disable SMT, so given that disabling SMT almost halves the performance on some workloads,¹ AMD is bound to have a huge performance advantage over Intel, on these particular workloads.

¹ For example in SPECvirt_sc2013 the patch reduces performance by 31% (https://www.servethehome.com/wp-content/uploads/2018/08/Inte...) 31% is unheard of for a security patch! It's a difficult security-speed tradeoff that businesses must carefully consider.