I've used memtest to find a bad byte of ram (12 digit hex address around 8100 th MB). I then added that address to /etc/default/grub 's GRUB_BADRAM section. I've uncommented GRUB_BADRAM and then run update-grub. It updated /boot/grub/grub.cfg and I can see the badram entry there. But it doesn't seem to take effect, my box still crashes due to the bad ram byte.
I've noted GRUB_BADRAM examples are all 8 hex digits but memtest reported the problem using 12 hex digits. How many digits should I use for GRUB_BADRAM ? Any other ideas of what am I doing wrong?