linux-aws fails to late load microcode, works with generic

[Dimitri John Ledkov]

[Impact]

 * Late loading of intel microcode doesn't seem to work on aws.

[Test Case]

 * Boot Focal on AWS metal instance
 * Install intel-microcode package
 * Disable early microcode loading:
   sudo rm /usr/share/initramfs-tools/hooks/intel_microcode to disable including microcde in the initrd
 * Update initrd
   sudo update-initramfs -u
 * Observe that late loading (due to /usr/lib/tmpfiles.d/intel-microcode.conf ) does not happen.

I.e. expected to see something like this:
$ journalctl -b | grep microcode
Feb 14 11:08:38 ottawa kernel: microcode: sig=0x506e3, pf=0x20, revision=0xc6
Feb 14 11:08:38 ottawa kernel: microcode: Microcode Update Driver: v2.2.
Feb 14 11:08:42 ottawa kernel: microcode: updated to revision 0xd6, date = 2019-10-03
Feb 14 11:08:42 ottawa kernel: x86/CPU: CPU features have changed after loading microcode, but might not take effect.
Feb 14 11:08:42 ottawa kernel: microcode: Reload completed, microcode revision: 0xd6

instead I see something like this:
Feb 14 11:08:38 ottawa kernel: microcode: sig=0x506e3, pf=0x20, revision=0xc6
Feb 14 11:08:38 ottawa kernel: microcode: Microcode Update Driver: v2.2.

(no updated to revivsion .... message)

[Regression Potential]

 * Late loading is new, as the current default is to load microcode early from initrd. It will only change behaviour on initrd-less bionic-minimal images, and any image types on later releases, but only when booted on the .metal instances.

[Steve Beattie (sbeattie)]

Hello Dimitri,

The source of this is that the linux-aws (and some other cloud-specific) kernels do not have CONFIG_MICROCODE_OLD_INTERFACE enabled, while they are enabled in the generic kernel configs.

For consideration, this is the kernel config documentation for this option:

  config MICROCODE_OLD_INTERFACE
        bool "Ancient loading interface (DEPRECATED)"
        default n
        depends on MICROCODE
        ---help---
          DO NOT USE THIS! This is the ancient /dev/cpu/microcode interface
          which was used by userspace tools like iucode_tool and microcode.ctl.
          It is inadequate because it runs too late to be able to properly
          load microcode on a machine and it needs special tools. Instead, you
          should've switched to the early loading method with the initrd or
          builtin microcode by now: Documentation/x86/microcode.rst

I'm going to mark this issue public. Thanks.

[Steve Beattie (sbeattie)]

Is this worth addressing in the cloud kernels or should we stick to early microcode loads only?

[Launchpad Janitor (janitor)]

[Expired for linux-aws (Ubuntu) because there has been no activity for 60 days.]