Linux 5.8 Adds initrdmem= Option For Cases Such As Replacing Intel ME Space With Initrd

Written by Michael Larabel in Linux Kernel on 1 June 2020 at 05:36 PM EDT. 9 Comments
One of the use-cases for this new "initrdmem" option in Linux 5.8 can be for storing an initial ramdisk (initrd) on a motherboard flash chip in the space available after stripping out Intel's Management Engine (ME) code.

The initrdmem= boot option can be used for specifying a physical address and size for loading an initrd embedded in memory. This new option was sent in as part of the x86/boot changes for the now-open Linux 5.8 merge window.

This option was added by Google's Ron Minnich, one of the original Coreboot/LinuxBIOS developers and project leader. In his patch for adding initrdmem, he outlines the interesting use-case for it of using leftover space on a flash chip after nuking Intel ME to instead have room for hosting the kernel and initrd image:
One such situation occurs when unused FLASH space on UEFI systems has been reclaimed by, e.g., taking it from the Management Engine. For example, on many systems, the ME is given half the FLASH part; not only is 2.75M of an 8M part unused; but 10.75M of a 16M part is unused. This space can be used to contain an initrd, but need to tell Linux where it is.

There are other possible uses for initrdmem= too in allowing the initrd to be placed in more areas, but this is one of the more interesting use-cases for this new addition.
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