On Fri, Oct 17, 2025 at 10:40:10PM -0400, Gregory Price wrote:
Under unknown conditions, Zen5 chips running rdseed can produce (val=0,CF=1) over 10% of the time (when rdseed is successful). CF=1 indicates success, while val=0 is typically only produced when rdseed fails (CF=0).
This suggests there is a bug which causes rdseed to silently fail.
This was reproduced reliably by launching 2-threads per available core, 1-thread per for hamming on RDSEED, and 1-thread per core collectively eating and hammering on ~90% of memory.
Which version of RDSEED was used? 32-bit perhaps? Can you repro this with the 64-bit version of RDSEED?
This was observed on more than 1 Zen5 model, so it should be disabled for all of Zen5 until/unless a comprehensive blacklist can be built.
As I said the last time, we're working on it. Be patient pls.
Thx.