AMD's Zen 4 has been tested with the various Spectre variant mitigations and the performance is surprisingly good. In fact, overall, the Ryzen 7950X has managed to beat the unpatched system.
Retpoline RSS
Testing the new retpoline mitigation on AMD for Spectre v2 shows that the performance loss with the new patch is nowhere nearly as big as the performance impact incurred by Intel processors.
Intel and ARM are vulnerable to the Spectre-BHB flaw, but AMD is apparently troubled by Spectre v2, which it should have fixed back in 2018. AMD has now issued a new fix for the CVE-2017-5715 bug.
A new CPU exploit based on the infamous Spectre v2 has been discovered. However, when the security patch is applied it can affect performance by up to 36%, that's according to a recent study.
Several versions of the Linux kernel have been patched with Retpoline which was made by a Google employee to mitigate against Spectre while keeping performance levels the same as they were before.
Google has announced that its cloud systems are not impacted with performance hits after it applied a patch dubbed Retpoline. Google plans to share the patch with others in the industry.