Status of PVH

sborrill

I have a NetBSD VM which was fully PV, but now has been upgraded to have a kernel which supports PVH. How do I configure the VM to use the PVH device model so I can get it to run now that vanilla PV is no longer supported?

--
Stephen

gduperrey

Have you seen this blog post?

https://xcp-ng.org/blog/2022/01/17/removing-support-for-32-bit-pv-guests/

There is a solution given in it in relation to this action.

TeddyAstie

We don't have a usable support for PVH guest at this time, though, for booting a PV guest on XCP-ng 8.3, you can enable PV-shim, e.g

xe vm-param-set uuid={UUID} domain-type=pv-in-pvh

sborrill

@TeddyAstie
Yes, I tried pv-in-pvh before posting and it didn't work. The VM appears to go through the starting process and then stops.

My theory is that this is because PV_LINEAR_PT is compiled out which is required by NetBSD PV. Even prior to this you had to enable it with:
/opt/xensource/libexec/xen-cmdline --set-xen pv-linear-pt=true

With the xl tool stack as used by a NetBSD dom0, pvshim does work with the same kernel.

TeddyAstie

@sborrill ouch that not practical
The command you provide doesn't work for pv-in-pvh.
A equivalent for the PV-shim would be

xe vm-param-add uuid={UUID} param-name=platform pvinpvh-xen-cmdline="pv-shim console=xen pv-linear-pt=true"

JeffBerntsen

@TeddyAstie Do you know if these can be set in XO or are they only via command line at this point? I'm curious and also curious as to how well supported because I'm looking at a possible migration from XS 7.1.2 to XCP-ng 8.3 where there are several 32-bit PV machines.

sborrill

@TeddyAstie Thanks, but that appears to make no difference

# xe vm-param-get uuid=82dfbfc3-d620-2aeb-8ac5-2567d44ea479 param-name=domain-type
pv-in-pvh
# xe vm-param-get uuid=82dfbfc3-d620-2aeb-8ac5-2567d44ea479 param-name=platform param-key=pvinpvh-xen-cmdline
pv-shim console=xen pv-linear-pt=true

TeddyAstie

@JeffBerntsen said in Status of PVH:

@TeddyAstie Do you know if these can be set in XO or are they only via command line at this point? I'm curious and also curious as to how well supported because I'm looking at a possible migration from XS 7.1.2 to XCP-ng 8.3 where there are several 32-bit PV machines.

It can be only be set from command-line for now. Though Xen Orchestra should be updated to convert to PV-in-PVH instead of between HVM and PV (this one being unsupported and not bootable anymore).

sborrill

@TeddyAstie Any idea how to debug this? I'd hoped that enabling VM console output with the following might help:

xenstore-write /local/logconsole/@ /tmp/console.%d.log

With the xl toolstack and pvshim, you see the shim xen kernel start on the VM serial console before handing over to the PV domU kernel. In XCP-ng, there is no output.

sborrill

PVH is supported just fine by the xl toolstack on XCP-ng and XenServer, so it's only the relevant glue missing in xapi to enable domain-type=pvh to work.

To demonstrate:

Download a NetBSD INSTALL kernel from https://ftp.netbsd.org/pub/NetBSD/NetBSD-10.1/amd64/binary/kernel/netbsd-INSTALL.gz to /root.
Create /root/nbpvh containing:

name = "nbpvh"
type="pvh"
kernel = "/root/netbsd-INSTALL.gz"
memory = 1024

Boot VM with xl create -c nbpvh

sborrill

@sborrill And for completeness, try pvshim (a.k.a. pv-in-pvh) using xl:

Download https://ftp.netbsd.org/pub/NetBSD/NetBSD-10.1/amd64/binary/kernel/netbsd-INSTALL_XEN3_DOMU.gz
Create /root/nbpv containing:

name = "nbpv"
type="pvh"
pvshim=1
pvshim_cmdline="pv-shim console=xen pv-linear-pt=true"
kernel = "/root/netbsd-INSTALL_XEN3_DOMU.gz"
memory = 1024

Boot VM successfully with xl create -c nbpv

So pv-in-pvh does work (does require pv-linear-pt=true on shim command line though).