Performance impact observed after Red Hat Enterprise Linux upgrade due to Speculative Return Stack Overflow (SRSO aka INCEPTION) CVE-2023-20569 vulnerability mitigations

Issue

Upgrading from a RHEL kernel without SRSO (CVE-2023-20569 aka INCEPTION) vulnerability mitigations to a kernel that does support SRSO mitigations may result in a performance impact. It has been observed on AMD Zen, generations 1-4. That is all families 0x17 and 0x19. Older processors have not been investigated.

This can happen when upgrading from older 8.x, or 9.x kernels without SRSO vulnerability mitigations to a newer RHEL kernel with SRSO vulnerability mitigations.