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Re: [Xen-users] CentOS 7 and PV HVM

  • To: "Steffan A. Cline" <steffan@xxxxxxxxx>
  • From: Wiebe Cazemier <wiebe@xxxxxxxxxxxx>
  • Date: Wed, 21 Mar 2018 10:04:40 +0100 (CET)
  • Cc: Xen-users@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Wed, 21 Mar 2018 09:06:08 +0000
  • List-id: Xen user discussion <xen-users.lists.xenproject.org>
  • Thread-index: aNa4lXr3B5ACUS/kvkuixlMP0cg1lw==
  • Thread-topic: CentOS 7 and PV HVM

----- Original Message -----
> From: "Steffan A. Cline" <steffan@xxxxxxxxx>
> To: Xen-users@xxxxxxxxxxxxxxxxxxxx
> Sent: Monday, 19 March, 2018 07:30:21
> Subject: [Xen-users] CentOS 7 and PV HVM

> With the changes in CentOS 7 not allowing for PV anymore, unless they fix it 
> as
> the Red Hat log indicates they may, in reading I’m hearing that PVHVM is the
> way to go offering more advantages.
> I tried using the configuration file shown on
> https://wiki.xen.org/wiki/Xen_Linux_PV_on_HVM_drivers but the errors returned
> are not very clear.
> Currently I am using the kernel Linux h1.hldns.com 4.9.75-29.el7.x86_64 #1 SMP
> Fri Jan 5 19:42:28 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux and the Xen
> 4.6.6-10.el7 packages
> Does anyone have a working config file for CentOS 7 I can try?

Can you post your current configs? I need to see what needs to happen to your 
disk volumes.

I'm currently in the process of converting all of our PV to HVM machines (which 
becomes PVHVM because of guest support). It involves creating new disk volumes 
with a grub stage1 and partition table, and then dd'ing the root volume into 
the partition.

I'm not sure if it's the only way in PV, but our PV machines don't have disks, 
only volumes; the PV guest doesn't have a disk with boot sector. That's why 
that's necessary.

We had to do the following on our Ubuntu PV DomUs (note, these are only for 
illustration, your situation will be different):

- which upstart-local-bridge && apt-get -o Dpkg::Options::="--force-confmiss" 
install --reinstall upstart # make VGA agetty work on upstart machines
- apt-get install grub2 (but say no to installing on /dev/xvdaX)
- update-grub2
- cp -a /usr/lib/grub/i386-pc/ /boot/grub/
- fstab -> change root partition (in my case /dev/xvda2) to UUID notation 
(found in /dev/disk/by-uuid)
- fstab -> comment and swap and fix later.
- update-initramfs -u

The config file needs minimal changes: set builder="hvm", change the disk 
volumes to a full disk, remove some superfluous statements (root directive, 
pygrub boot loader, etc).

Once booted in VM:
- update-grub2
- grub-install /dev/xvda
- fix swap (mkswap /dev/xvda2 and correct fstab in my case)
- reboot

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