Public bug reported:

[Impact]

Cirtain EFI systems will no longer boot with updated versions of maas.
They will still boot in BIOS compatibility mode where available.

[Test Case]

Affected systems have already been tested with this fix applied and now
boot successfully in EFI mode.  The key test is does any EFI based
system boot with this applied.

[Regression Potential]

The change increased the headroom by a very small amount, an additional
8 slots.  This is very unlikely to lead to additional failures.

===

When booting via newer versions of maas we use grub extensions to load
additional files.  This leads the kernel to panic in efi_main():

     exit_boot() failed!
     efi_main() failed!

This occurs because the EFI memory map is more fragmented.  When we exit
boot services that returns an updated memory map in a buffer we supply.
This has to be large enough to contain the updated map.  If the exit
fails because of lack of map space we are dead in the water because the
call to allocate memory is lost to us.  We therefore add some headroom
in the allocation to allow for any expansion during close.  This
headroom is insufficient.

** Affects: linux (Ubuntu)
     Importance: High
     Assignee: Andy Whitcroft (apw)
         Status: In Progress

** Affects: linux (Ubuntu Bionic)
     Importance: High
     Assignee: Andy Whitcroft (apw)
         Status: In Progress

** Affects: linux (Ubuntu Disco)
     Importance: High
     Assignee: Andy Whitcroft (apw)
         Status: In Progress

** Affects: linux (Ubuntu Eoan)
     Importance: High
     Assignee: Andy Whitcroft (apw)
         Status: In Progress

** Affects: linux (Ubuntu Focal)
     Importance: High
     Assignee: Andy Whitcroft (apw)
         Status: In Progress

** Changed in: linux (Ubuntu)
       Status: New => In Progress

** Changed in: linux (Ubuntu)
   Importance: Undecided => High

** Changed in: linux (Ubuntu)
     Assignee: (unassigned) => Andy Whitcroft (apw)

** Description changed:

+ [Impact]
+ 
+ Cirtain EFI systems will no longer boot with updated versions of maas.
+ They will still boot in BIOS compatibility mode where available.
+ 
+ [Test Case]
+ 
+ Affected systems have already been tested with this fix applied and now
+ boot successfully in EFI mode.  The key test is does any EFI based
+ system boot with this applied.
+ 
+ [Regression Potential]
+ 
+ The change increased the headroom by a very small amount, an additional
+ 8 slots.  This is very unlikely to lead to additional failures.
+ 
+ ===
+ 
  When booting via newer versions of maas we use grub extensions to load
  additional files.  This leads the kernel to panic in efi_main():
  
-      exit_boot() failed!                                                      
                                               
-      efi_main() failed!                                                       
                                               
+      exit_boot() failed!
+      efi_main() failed!
  
  This occurs because the EFI memory map is more fragmented.  When we exit
  boot services that returns an updated memory map in a buffer we supply.
  This has to be large enough to contain the updated map.  If the exit
  fails because of lack of map space we are dead in the water because the
  call to allocate memory is lost to us.  We therefore add some headroom
  in the allocation to allow for any expansion during close.  This
  headroom is insufficient.

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https://bugs.launchpad.net/bugs/1851810

Title:
  Some EFI systems fail to boot in efi_init() when booted via maas

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