[Bug 1508893] Re: TFTP timeout on ARM64 hw when booting from grub that was PXE loaded

[dann frazier]

I applied just this patch to wily's grub and tested on a thunder
platform w/ AMI UEFI, and it appears to have introduced a regression.
Where a MAAS boot would work successfully before, it now triggers a
Synchronous Exception.

The attached script will create a grub netboot image the same way MAAS
does.

** Attachment added: "script to generate a MAAS-like grubaa64.efi"
   https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1508893/+attachment/4502594/+files/make-image.sh

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https://bugs.launchpad.net/bugs/1508893

Title:
  TFTP timeout on ARM64 hw when booting from grub that was  PXE loaded

Status in grub2 package in Ubuntu:
  New

Bug description:
  This issue was discovered  with Ubuntu Wily (15.10) on a currently in
  development ARM64 HW.

  When loading kernel via tftp in grub on this hardware, the system
  stops receiving new packets (times out )  after receiving initial few
  tens of tftp data packets , which then causes kernel load failure.

  Running tcpdump before loading kernel in grub menu shows timeouts
  occurring,  as captured in the below log  :

        http://kernel.ubuntu.com/~ming/grub/apm.tcpdump

  Following are the  detailed reproduction steps :

  1) setup PXE boot entry in UEFI(no any parameter to grub)
  2) build one grub from upstream (and/or Wily)  and put it in PXE&TFTP server
  3) setup grub config, suppose the shape is like below:
       menuentry 'Install for arm64' {
            linux /ubuntu-installer/arm64/Image --- console=ttyS0,115200
            initrd /ubuntu-installer/arm64/initrd.gz
      }
  4) start PXE booting in UEFI
  5) grub prompt is coming
  6) select 'Install for arm64' menu item and press 'enter' to start
  loading kernel
  7) then hangs inside loading kernel

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