AMD Sends Out Linux Kernel Patches To Allow Disabling Predictive Store Forwarding (PSF)

AMD last week published a security whitepaper on Zen 3's Predictive Store Forwarding (PSF) functionality introduced with Ryzen 5000 series and EPYC 7003 series processors. In the whitepaper they mentioned Linux patches were published for allowing this feature to be disabled if concerned about the security risk, well, today those patches were made public.

Hitting the Linux kernel mailing list today were the five patches for mitigating Predictive Store Forwarding if desired. With a patched kernel, PSF remains on by default but can be disabled via the Spectre V4 mitigation control or by setting the nopsfd kernel parameter boot option to just force off this feature. Again, this is only relevant for Zen 3 (and presumably future) CPUs.

AMD doesn't believe there is much real-world security risk but for those concerned the option is available. My initial PSF benchmarking found minimal performance impact when disabling it. Ongoing tests have shown no measurable difference outside of some long-running database workloads where even there was just 1~2% or less. So overall the exposure seems to be quite minimal even if you want to disable it.

The AMD PSF patches out now for public review can be found on the kernel mailing list.