Ahead of the Linux 6.16-rc6 kernel release due out later today, an x86/urgent pull request was sent out today that includes some fixes for old AMD Zen 2 hardware.
There are two principal set of changes with this week’s “x86/urgent” pull request for the ongoing Linux 6.16 cycle. First up, it contains patches for updating the MAINTAINERS entry with longtime Linux engineer Kirill Shutemov leaving Intel and thus transitioning to his personal email address. The other x86/urgent change this week is:
“- Add fixes for a misconfigured AMD Zen2 client which wasn’t even supposed to run Linux”
What is this old AMD Zen 2 client that “wasn’t even supposed to run Linux”? The AMD BC-250 mining card with the Cyan Skillfish Zen 2 era APU.
Yes, the Cyan Skillfish APU graphics have long been supported by the upstream AMDGPU open-source driver while these latest changes are about the Zen 2 cores found with the BC-250.
The fixes merged for Linux 6.16 and also back-porting to prior stable kernel versions is to disable RDSEED usage on Cyan Skillfish APUs and to also disable INVLPGB usage on Zen 2 CPUs.
The Zen 2 cores on Cyan Skillfish have an issue where RDSEED usage always returns 0xffffffff while RDRAND usage works correctly. The fix for Linux will advertise RDSEED as not being exposed for the platform. Not too surprising for Linux users with random number generation issues in the early Zen days being a common occurrence. Fortunately there haven’t been RdRand/RDSEED issues in newer generations like there was with the older cores.
The other issue is that BC-250 has been running into issues since Linux 6.15 when beginning broadcast TLB invalidation for multi-threaded processes. That ends up breaking the BC-250 from booting Linux with a kernel oops. AMD INVLPGB can yield some nice performance benefits with newer AMD cores at least and was upstreamed in Linux 6.15. Due to the issues on Cyan Skillfish, INVLPGB usage is being disabled for Zen 2 Family 17h, Model 47h cores.
So with these patches in x86/urgent that will be found in today’s Linux 6.16-rc6 kernel release and also back-ported to stable kernel branches, Linux support for the Zen 2 cores on the Cyan Skillfish APU within the BC-250 should be playing nicely.
