[Pkg-libvirt-maintainers] Bug#1120807: virt-install: fails to create ppc64el machines due to page size choice

[Helmut Grohne]

On Tue, Nov 18, 2025 at 08:04:08AM +0100, Bastian Blank wrote:
> On Sun, Nov 16, 2025 at 08:20:31AM +0100, Helmut Grohne wrote:
> > I tried using virt-install to create a ppc64el kvm virtual machine. This 
> > fails with an error relayed from qemu:
> > | Can't support 64 kiB guest pages with 4 kiB host pages with this KVM implementation
> 
> This is a bug in qemu, see #1107288.

As far as I read that bug, this is being disputed and does not look like 
it is being fixed there. The reasoning roughly goes like qemu wants to 
have repeatable behavior. I note that users can already opt out of 
repeatable behavior e.g. via -cpu max. Indeed, if you were to create a 
VM with a 64kiB kernel and then run it in autodetection, it might work 
or not.

Generally, qemu seems to have very user-unfriendly defaults in a lot of 
areas. For instance, the default for -m is 128M. There are reasons for 
that, but to me it seems like it is to be expected that users have to 
override a lot of parameters to make it practically useful (which is 
what e.g. debvm does).

Conversely, my impression is that higher level interfaces (debvm, 
libvirt) are expected to paper over this and to me that includes the 
page size matter at hand. I'm not sure virt-install should autodetect 
this, but I think it should expose it in a way that does require 
--qemu-commandline.

At the same time, I relate to the view that maybe qemu could out of its 
way and provide the user with an explicit choice of "yes, I want an 
unpredictable page size" while not making that the default.

Helmut