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

  • To: xen-users@xxxxxxxxxxxxxxxxxxxx
  • From: Andy Smith <andy@xxxxxxxxxxxxxx>
  • Date: Mon, 18 Jan 2021 13:50:49 +0000
  • Delivery-date: Mon, 18 Jan 2021 13:51:31 +0000
  • List-id: Xen user discussion <xen-users.lists.xenproject.org>
  • Openpgp: id=BF15490B; url=http://strugglers.net/~andy/pubkey.asc


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.




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