Fedora switched to zstd kernel compression, may cause PV mode booting difficulty

[Andy Smith <andy@xxxxxxxxxxxxxx>]

Hi,

As of kernel-core-5.9.8-100.fc32.x86_64.rpm, Fedora switched from
gzip compression to zstd for their kernel. pvgrub doesn't support
this, so if you're using that you'll be in a similar position as
with Ubuntu 19.10+ which switched to lz4.

As pvgrub hasn't got lz4 support yet it seems unlikely it will get
zstd support either.

As with Ubuntu, I found it easiest to switch such guests to PVH mode
booted with pvhgrub. pvhgrub uses the standard grub kernel loading
methods so lz4 and zstd are both fine.

I have not tested direct kernel booting of zstd kernels, neither PV
nor PVH. If direct booting works then I guess pygrub would as well,
but anyone who moved off of pygrub probably doesn't want to go back.

Cheers,
Andy