More AMD Family 19h (Zen 3) Code Trickling Into Linux 5.7
For Linux 5.6 has been some Family 19h PCI IDs being added to existing AMD Zen support code paths. Last month were a few 19h patches for the perf subsystem.
The latest is a patch now queued in the x86/cpu branch ahead of the Linux 5.7 merge window opening in a few weeks. That patch is extending the AMD kernel code to now also call the AMD Zen init function (init_amd_zn()) for Family 19h CPUs. "Family 19h CPUs are Zen-based and still share most architectural features with Family 17h CPUs, and therefore still need to call init_amd_zn() e.g., to set the RECLAIM_DISTANCE override."
The patch also confirms Family 19h "Zen 3" has the same mitigation handling around SSBD (Speculative Store Bypass Disable / Spectre V4). Also, the patch confirms Family 19h isn't impacted by the earlier Zen CPU erratum around the Core Performance Boost (CPB) bit potentially not being set. Neither of those bits of information come as a surprise and no juicy details revealed as part of these Family 19h patches so far.
We'll see what other AMD Family 19h support gets squared away in time for Linux 5.7. If this flow of Family 19h patches keep up, the support should get ironed out in time for offering nice out-of-the-box support by the Linux distribution releases this fall (Ubuntu 20.10, Fedora 33, etc). AMD Zen 3 processors are expected to begin shipping later this calendar year.
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