> Blah. I'm running Linux with ext4 on my Samsung SSD 840 EVO 250GB (EXT0BB6Q).
> Am I totally screwed?
Not totally as long as your chipset is supported, but almost.
All you need to do is extract actual SSD firmware upgrade file from Windows executable, then create freedos bootable USB stick, copy DOS updater files extracted from older Samsung DOS updater download and add those new SSD firmware from new Windows updater to your custom upgrade USB stick. After you have managed to upgrade SSD firmware boot system using some live linux and do non-destructive badblocks read+rewrite scan over entire SSD.