“According to Intel, some workloads may experience up to 50% overhead.”
Intel’s Gather instruction leaks the vector register file during speculative execution on every Core chip from 6th-gen Skylake through 11th-gen Tiger Lake. Moghimi built an end-to-end attack that steals OpenSSL keys in two weeks. Intel holds more than 70% of the server market, so a malicious cloud neighbour is the realistic attacker. Off-the-shelf antivirus cannot see it. Intel sold that speed years ago and now the fix takes up to half of it back.