Re: [BUG] KHO handover hangs when memmap reserves PMEM

[Chris Bainbridge <chris.bainbridge@canonical.com>]

On Tue, Oct 06, 2026 at 12:55:31PM +0200, Mike Rapoport wrote:
> On Sat, Oct 03, 2026 at 06:02:27PM +0100, Chris Bainbridge wrote:
> > Hello,
> > 
> > I am reporting a regression in KHO handover.
> > 
> > In the most recent Ubuntu 26.10 beta mini-ISO releases (2026-09-18 onwards),
> > the first kernel reserves RAM for the downloaded ISO with a memmap directive
> > such as memmap=<size>!4G, then kexecs a second kernel. On affected kernels, the
> > first kernel reaches "kexec_core: Starting new kernel", but the second kernel
> > produces no further output and QEMU spins at 100% CPU. On unaffected kernels,
> > the second kernel starts and finds /dev/pmem0 with the expected "Persistent
> > Memory (legacy)" range in /proc/iomem.
> 
> TO make sure I understand this correctly, you enable KHO in the builds of
> the installer kernel and then the installer command line explicitly enables
> KHO.

Yes.

> Is there anything you actually preserve with KHO when kexec'ing the second
> kernel?

No. kho=off is a valid workaround for the mini ISO. I only reported it
as a regression here because this was working until the bisected commit
was merged. If this is intended behaviour then it is not a problem.