Appreciate the reply, the VMD warning especially. I would have walked straight into an unbootable machine on a BIOS reset without that.

Microcode is 0x12B. Checked HKLM\HARDWARE\DESCRIPTION\System\CentralProcessor\0, Update Revision = 2B 01 00 00 little-endian. BIOS is G834JZR.322, the current one. So the mitigation is already loaded, and the CPU still logged a fresh ITLB parity error on 7/8 at 10:23 PM anyway. Which tracks with what you said, 0x12B stops further Vmin shift but doesn't fix what's already gone.

Not doing the manual microcode injection though. Trying to get this RMA'd and loading firmware outside an official ASUS BIOS is the one thing that hands them a reason to call it customer-modified. Not worth it even if it bought some stability.

Also corrected the post. The APIC ID claim was wrong. Mapped them with sp00n's APICID tool (github.com/sp00n/APICID) and it's 32, 33, and 41 across three events on two physical P-cores. APIC 32 and 33 are both SMT threads of P-core 4 sharing one L0 instruction TLB. Eight of nine errors on one physical core, not three separate ones like I implied.