Re: Urgent: NetBSD domUs will not start after Xen kernel update

[John Nemeth <jnemeth%cue.bc.ca@localhost>]

On Oct 23,  6:33pm, Manuel Bouyer wrote:
} On Mon, Oct 23, 2017 at 05:14:10PM +0100, Stephen Borrill wrote:
} > Thanks for your quick reply. I can confirm that the following command gets
} > VMs booting again:
} > /opt/xensource/libexec/xen-cmdline --set-xen pv-linear-pt=true
} > 
} > i.e.
} > # xl info | grep commandline
} > xen_commandline        : dom0_mem=752M,max:752M watchdog ucode=scan dom0_max_vcpus=4 crashkernel=128M@256M console=vga vga=mode-0x0311 pv-linear-pt=true
} > 
} > However, while this is a useful workaround, it's not great going forward as
} > the command line may be modified when other hotfixes or upgrades happen (or,
} > of course, may not be under your administrative control). What's the roadmap
} > for fixing this in the NetBSD kernel?
} 
} The x86 pmap makes heavy use of linear mappings, so it's not going to be
} "fixed" anytime soon (actually I consider it's a bug in Xen that it is
} disabled by default).

     Also, PV mode is effectively obsolete.  Given that page table
handling is at the very lowest level of the kernel and is quite
complicated, I don't see NetBSD ever "fixing" this.  I consider
that it was rather rude of upstream to do something knowing that
it would break NetBSD in order to work around their bug.

     There is on-going work to make NetBSD work in PVHVM mode for
domU and PVH mode for dom0.  Once this work is completed, there
will be no need to use PV mode except for older versions of NetBSD
and/or older versions of Xen.  Since PV mode can be effectively
considered to be a "compatible" mode, there is no reason to spend
huge effort on maintaining it.  Minor effort where useful is a
different thing.

}-- End of excerpt from Manuel Bouyer