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Re: Kernel modules on 10.1



On Wed, 19 Mar 2025, Brad Spencer wrote:
Stephen Borrill <netbsd%precedence.co.uk@localhost> writes:

[snip]

Support for PVH is somewhat vague in the xapi toolstack (XenServer,
XCP-ng). I have tried a NetBSD 10.1 PV VM that works on earlier versions
on the latest XenServer 8.4. It fails to start in PV mode with the
following error:
Domain.Domain_build_pre_failed("Calling 'shadow_allocation_set 10 MiB'
failed: Xenctrl.Error(\"22: Invalid argument\")")

I think this is because of the following change as part of the update to
Xen 4.17:

- PV32, PV_LINEAR_PT and SHADOW_PAGING now compiled out

(from https://koji.xcp-ng.org/buildinfo?buildID=3568 )

It looks like you can set domain-type=pv-in-pvh on the VM (even it is only
documented having pv and hvm values). This does attempt to start the VM,
but it stops quickly afterwards. Perhaps this is because of PV_LINEAR_PT
being removed or is this not relevant with PVH mode?

Something called 'pv-in-pvh' sounds like pvshim.  I don't know what this
particular provider does for configs, but on self hosted Xen, you have
to put the following in the Xen config to get pvshim to work:

.
.
type="pvh"
pvshim=1
.
.


This will run a pure PV guest in a PVH container which runs under the
hypervisor.  It is a way to get some more security and maybe performance
out of a PV guest that can't do PVH or PVHVM itself.

I think (without much proof) that pv-in-pvh would work, but as part of the upgrade to 4.17 PV_LINEAR_PT is now compiled out. Previously it was disabled, but could be enabled from the dom0 boot config with:
/opt/xensource/libexec/xen-cmdline --set-xen pv-linear-pt=true

NetBSD PV requires PV_LINEAR_PT to boot unfortunately, therefore even with pvh/pvshim booting will fail.

So some compiled out settings stop pure PV booting and others stop PVH.

Just for the record this isn't a 'provider' issue. xapi is an equally open-source and official toolstack for Xen (and self-hosting) as the xend toolstack we used in NetBSD; it's just a lot more featureful and heavyweight.

--
Stephen


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