On AWS, mount the root volume to another host and arch-chroot.
Need package arch-install-scripts package installed to run arch-chroot.

To avoid this situation, TAKE SNAPSHOT BEFORE DOING ANY KERNEL UPDATES!

Record bad kernel version at start.
TODO:  Verify that chrooted root volume kernel version by running
    pacman -Q | grep linux
    chroot /mnt; pacman -Q | grep linux

Revert to an older kernel by: cd /var/cache/pacman/pkg
Hopefully there's a recent version to revert to.
ls -ltr linux*  (use wildcard to narrow to only the base kernel package)
pacman -U linux-specific*