On Sun, Nov 16, 2025 at 08:20:31AM +0100, Helmut Grohne wrote: > Package: virt-install > Version: 1:5.0.0-5+deb13u1 > X-Debbugs-Cc: [email protected], [email protected] > User: [email protected] > Usertags: ppc64el > > Hello, > > 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 > > The default machine used by virt-install for ppc64el is "pseries" and it > appears to default to 64 kiB guest pages. Debian has changed (#1074217) > the kernel's page size to 4 kiB for trixie though, so that's what Debian > hosts typically use. > > On the qemu side, we may change this by passing: > > -machine pseries,cap-hpt-max-page-size=4096 > > Now getting this option through virt-install is not obvious. Trying to > pass a machine with an option to virt-install's --machine option results > in a failure as it interprets the combination of machine and option as > the machine and has no clue about this machine. > > A workaround here is passing it as a --qemu-commandline. > > --machine=pseries "--qemu-commandline=-machine > pseries,cap-hpt-max-page-size=4096" > > Would it be possible for virt-install to support this use case in a more > convenient way? For instance, it could detect the host's page size and > adjust it itself or it could enable passing such options via --machine. > > Thanks for considering
So, a few things.
First of all, libvirt already exposes this capability: use
<domain>
<features>
<hpt>
<maxpagesize unit='KiB'>4</maxpagesize>
...
to configure it.
virt-install doesn't seem to support manipulating this value
directly though, at least based on the output of
$ virt-install --features help
so an upstream RFE will need to be filed to make that happen.
Taking a step back though, shouldn't QEMU default to a 4k page size
when 64k cannot work on the host?
Maybe there's something in the sPAPR spec that mandates 64k as the
default, I don't know. That would be very unfortunate. Users should
really not need to be aware of this kind of detail just to get a
basic VM going.
--
Andrea Bolognani <[email protected]>
Resistance is futile, you will be garbage collected.
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