[Bug 1911439] Re: Netboot improvements backport from hirsute

[Dimitri John Ledkov]

Side loaded 2.04-1ubuntu26.8 onto MAAS and deployed machines in UEFI
secureboot mode. They boot fine.

Also upgraded the deployed machine to 2.04-1ubuntu26.8 as well. And
boots fine.

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** Tags added: verification-done-focal

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Title:
  Netboot improvements backport from hirsute

Status in grub2 package in Ubuntu:
  Fix Released
Status in grub2 source package in Focal:
  Fix Committed
Status in grub2 source package in Groovy:
  Fix Committed
Status in grub2 source package in Hirsute:
  Fix Released

Bug description:
  [Impact]

   * There have been multiple reports on netboot failures using
  grubnetx64.efi. This backport attempts to cherrypick multiple patches
  to improve the netboot speed and hopefully reliability. Also timeouts.

  TCP window scaling is improved for faster data transfers.
  Support for larger link layer addresses is added.
  tsc-calibration is sped up - as it can take up to 51s currently for grub to fail to calibrate on some hardware configurations.

  All of the above should not break network boot deployments, and
  hopefully make them more reliable. Reliability of deployments is yet
  to be determined however.

  [Test Case]

  Let's ensure that network stack and network deployments still operate
  correctly.

   * Deploy MAAS

   * In /var/snap/maas/common, find the symlinks to grubx64.efi file
  which is signed grub net x64 EFI prebuilt app from grub2-signed
  package

   * Replace it with the /usr/lib/grub/x86_64-efi-
  signed/grubnetx64.efi.signed file from the grub2-signed package

   * Deploy a UEFI machine with MAAS

   * Observe that deployment is successful.

  [Where problems could occur]

   * The networking code in grub is changed, thus issues could happen in
  the network deployments of grub over pxe-boot / uefi-boot and similar.
  For example some machines/cards may have started to work (and
  previously didn't, and ended up booting off local drive) or stopped to
  work (thus failing to boot remotely).

  [Other Info]

   * These changes have been tested in MAAS on x86 UEFI already using
  the hirsute build of grub2.

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