I got it fixed! In the BIOS I ran quick diagnostic test (includes a memory check). No problems were indicated, but the next time I booted the machine (using Ubuntu 21.04 on a USB stick) the memory seemed normal again. All memory available. And it has worked ever since, independent on whether I boot from a stick or from the fixed disk.
So, most likely the diagnostic test touched something, after which it started working. (Probably trying newer version of Ubuntu live from USB stick had no part in this:) -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1944019 Title: Most of the computer's memory rendered unavailable in Linux after updating BIOS To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1944019/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
