Mailing List Archive

Fedora switched to zstd kernel compression, may cause PV mode booting difficulty
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
Re: Fedora switched to zstd kernel compression, may cause PV mode booting difficulty [ In reply to ]
On Mon, Jan 18, 2021 at 01:50:49PM +0000, Andy Smith wrote:
> I have not tested direct kernel booting of zstd kernels

I see the patches by Jan for that on xen-devel now, so I guess
that's going to be a 4.15 feature.

Cheers,
Andy