SLES 15 and the inability to boot the Xen kernel

I had to face a funny error, according to which I could not immediately find any information on the Internet.

This is the problem in the first place. SUSE Linux Enterprise Server 15 is loaded, reaches the GRUB boot menu. Further, if you select a regular kernel, everything is fine, but if you select a kernel for the Xen hypervisor, the screen blinks and we return to the menu again. There is no way to start Xen.

Long exercises with GRUB settings and kernel boot parameters did not give anything (and it should be noted that initializing the server at boot is a slow process, so the process drags on for a long time). Finally, there was a thought leading to victory – to shoot the download process on a smartphone in an accelerated mode!

After several attempts, I managed to get this frame:

This image is kept on the screen in the best case of a split second.

Then it was a matter of technology to find description of the problem on the Lenovo support forumwhich is as follows.

The Xen kernel EFI bootloader is loosely written, and loads the kernel with a single physical read instruction.
Prior to SLES 15 SP2, the kernel size was just under 16 megabytes, starting with SP3 it has increased to just over 16 megabytes.
For a number of controllers and disks, the size of the read buffer is limited to exactly 16 megabytes.
As a consequence, booting Xen in EFI mode from an underdeveloped controller or disk results in a read error and an immediate return to the menu.

In order to cope with the problem, it is proposed to use one of the following solutions:

a) Wait for the Xen community to fix the bug by integrating Lenovo/IBM suggestions into their code (nothing has happened since 15SP3, now it’s 15SP5).

b) Download the Xen kernel sources and recompile with the patch suggested on the support page mentioned above, where the file is read in 1MB chunks (didn’t test it, but should work).

c) Boot the server not in EFI mode, but in Legacy mode (it works).

A very instructive story.