Re: Utility of PV on non-obsolete hardware

[T <bobs%thelibertytree.org@localhost>]

On 4/4/19 11:14 AM, Greg Troxel wrote:
> A good start would be someone who is running PVHVM or HVM mode sending a
> note to this list with:
>
>    which netbsd and xen versions support what they are doing, or which
>    versions they know support it
>
>    what goes in the config file that's different from the (pv) examples
>
> We don't need anything fancy.  Somebody who understands who takes 5
> minutes to send the above message, and somebody willing to edit the wiki
> for 15 minutes is all we are talking about.

I've been using HVM mode with a [Xen 4.11(from pkgsrc)/NetBSD 8.0 
Dom0/LVM storage backend] setup because PV mode resulted in to many 
problems. For my particular use case, I need to be able to access the OS 
GUIs from the VMs. This could not be done with NetBSD 8.0 in PV mode, 
because the Xen vfb does not appear to be supported. HVM mode had to be 
used for that reason alone. Trying to install NetBSD 8.0 in PV mode from 
a mounted ISO would have lengthy freeze ups during the sysinst process 
for whatever reason.

The following config is what I've found to work, which is slightly 
different from the example configuration file (xlexample.hvm) that can 
be found in:
/usr/pkg/share/examples/xen/


----FILE-START----
# This configures an HVM rather than PV guest
builder="hvm"

# Guest name
name="NetBSD01.hvm"

# 128-bit UUID for the domain as a hexadecimal number.
# Use "uuidgen" to generate one if required.
# The default behavior is to generate a new UUID each time the guest is 
started.
#uuid="XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX"

# Enable Microsoft Hyper-V compatibile paravirtualisation /
# enlightenment interfaces. Turning this on can improve Windows guest
# performance and is therefore recommended
#viridian=1

# Initial memory allocation (MB)
memory=8192

# Maximum memory (MB)
# If this is greater than `memory' then the slack will start ballooned
# (this assumes guest kernel support for ballooning)
#maxmem=8192

# Number of VCPUS
vcpus=2

# Network devices
# A list of 'vifspec' entries as described in
# docs/misc/xl-network-configuration.markdown
vif=[ 'mac=00:00:00:d0:0d:01, bridge=bridge0' ]

# Disk Devices
# A list of `diskspec' entries as described in
# docs/misc/xl-disk-configuration.txt
disk=[ '/dev/mapper/vg0-NetBSD01,raw,xvda,w',
#          '/dev/cd0,raw,xvdb,r,cdrom' ]
'/home/myuser/OS/NetBSD-8.0-amd64-install.iso,raw,xvdb,r,cdrom' ]
#          '/tmp/flatFile.xvd,raw,xvdb,w' ]

# Guest VGA console configuration, either SDL or VNC
vga='stdvga'
#sdl=0
vnc=1
vncpasswd='something'
vnclisten = "0.0.0.0"

# Fix for mouse sync issue
usbdevice='tablet'

# boot on floppy (a), hard disk (c) or CD-ROM (d)
# default: hard disk, cd-rom, floppy
boot="dc"
----FILE-END----

The mouse driver fix is needed because it will be barely usable in VNC 
without it. I do not believe this is mentioned in the NetBSD or Xen 
Project documentation. It appears that Citrix XenServer has this setting 
enabled by default so it is likely not a Dom0 OS specific issue. The vga 
setting is specified so the video driver RAM uses 8MB instead of the 
default 4MB(cirrus driver).

There are a few other issues that beginners may run into, because 
they're not mentioned in the NetBSD Xen documentation:
- UEFI booting of Xen does not work with a NetBSD Dom0 (as of 8.0) 
because Multiboot functionality has not yet been implemented. Xen can 
still be booted using the LegacyBIOS mode. A GPT partitioned drive can 
still be used, but it will need a MBR. I sent an email about this before.

- If using LVM as a storage backend, be sure to use path format 
"/dev/mapper/[volumeGroup]-[partionName]" instead of 
"/dev/[volumeGroup]/[partitionName]" in the configuration file or else 
Xen will not be able to open the partition when creating the VM.

- Also be aware that LVM in NetBSD is currently lacking snapshot 
functionality.

- The diskspec format has changed, the one used in the NetBSD 
documentation is the deprecated format. See here:
https://xenbits.xen.org/docs/4.3-testing/misc/xl-disk-configuration.txt

Hope this helps,
-Tim