Comment 15 for bug 1955655

I believe this is still related to lack of rhboot upstreaming patches to grub to use highmem allocations; such that lowmem remains unused; and thus SEV/SWIOTLB can be used "normally".

It is likely the difference you see is due to fedora's grub patches.

It would be interesting, if you could unpack & use fedora's kernel with ubuntu's grub, and see if fedora's kernel starts failing when booted via ubuntu's grub?

Or vice-versa; unpack and use ubuntu's kernel on fedora with fedora's grub to observe it working fine.

That would help eliminate differences of grub between the distros with the same kernels.