System boot ends in Grub Out of Memory (OOM)

Abstract

In the Secure boot environment, GRUB2 currently negotiates with PowerVM to allocate a 512 MB memory region, known as the Real Mode Area (RMA), for boot memory. The RMA must be large enough to hold the Linux kernel, initramfs, Partition Firmware (PFW), GRUB2, and working memory for early Linux boot. The region is divided among the boot components and, if any component exceeds its allocation, out-of-memory failures occur.

Currently, PFW is approximately 130 MB, leaving approximately 382 MB for the other boot components. The Linux kernel and GRUB2 each claim one-fourths of the 382 MB area, providing each with approximately 95 MB. If either the kernel image or the initramfs requires more than 95 MB, then GRUB2 might fail with an out-of-memory error when it attempts to load them.

Generally, the default installed initramfs and vmlinux are well within the limits to avoid such issues, but if Firmware Assisted Dump (FADump) is enabled in the system, the default initramfs size might increase and go beyond 95 MB. In that case, every system reboot ends up in a GRUB OOM issue.

To avoid this issue, do not use secure boot and FADump together. Otherwise, you can use one of the fixes available in the Workaround section.