Bug#1079800: Bug#1107288: qemu-system-ppc - kvm configured incorrectly for debian: Can't support 64 kiB guest pages with 4 kiB host pages

Hi,

On Thu, Jun 05, 2025 at 03:22:28PM +0200, Bastian Blank wrote:
> Control: severity -1 serious
> 
> On Wed, Jun 04, 2025 at 10:29:09PM +0200, Bastian Blank wrote:
> > qemu is configured to always request 64 KiB pages on ppc64(el).  Debian
> > does not (longer) support this mode by default.  This means qemu needs
> > to automatically downgrade to 4 KiB if this is the only thing that's
> > supported.
> 
> This now means that qemu with kvm is completely broken on ppc64el.  How
> should we fix that?
> 
> - Breaks on the kernel, with what?
> - Disable kvm in the kernel?

Why would we disable kvm in the kernel in that case, just because qemu
does not work with stock defaults - given that you can always disable
kvm in qemu?

Anyway: On one of the DSA machines I ran into this issue and the
Internet told me to pass "-machine pseries,cap-hpt-max-page-size=4096"
to qemu, which seems to work just fine under trixie's 4k default kernel.

It'd be great if qemu could autodetect this, i.e. presumably use
getconf(PAGE_SIZE) for this.

Kind regards
Philipp Kern