Banks for the Machine Check Architecture are a means of organizing subsystems/subevents with their relevant MSRs for detecting/reporting machine errors. Older processor families had only a few banks of registers for machine check support while the current limit in the AMD MCE driver has been 32 banks. With a patch queued in ras/core ahead of Linux 5.10, that maximum number of banks is being increased from 32 to 64.
The patch by one of AMD's engineers simply notes, " Increase maximum number of banks to 64 because future AMD systems will support up to 64 MCA banks per CPU. "
It will be interesting to see what's in store with the machine check improvements for future AMD CPUs, which given the timing will likely be with Zen 3 server CPUs.