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Re: [Xen-users] PV Drivers in Linux HVM DomU?

  • To: "Pasi Kärkkäinen" <pasik@xxxxxx>
  • From: "Emre Erenoglu" <erenoglu@xxxxxxxxx>
  • Date: Thu, 22 Nov 2007 18:48:26 +0100
  • Cc: Xen Users <xen-users@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Thu, 22 Nov 2007 09:49:15 -0800
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Hi Pasi, thanks again for your response. Answers below:

On Nov 22, 2007 5:36 PM, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
On Thu, Nov 22, 2007 at 03:57:23PM +0100, Emre Erenoglu wrote:
> >
> > > Or, does the recent introduction of VMI into the linux kernel make this
> > > automatic for us? i.e. if I use any recent kernel, such as Ubuntu's
> > > 2.6.22-14-generic, will paravirtualized disk/network drivers be
> > > automatically activated?
> > >
> >
> > VMI is VMware's interface to run paravirtual Linux on VMware. It doesn't
> > work or help at all with Xen.
> Well maybe I stated wrong, i was mentioning VMI (or whatever function it is)
> as a common way to enable standard kernels to work as Paravirtual when they
> detect the presence of a hypervisor. I think this is now standard for all,
> including VMWare and XEN.

This standard paravirtualization layer/support is called "paravirt ops" in kernel.

"paravirt ops" is then implemented for Xen, VMI, KVM, Lguest etc..

> FYI, it is possible to boot a 2.6.23 vanilla kernel as paravirtual DomU, but
> my question was if the paravirtual drivers were already there if I use HVM
> instead of Paravirtualization. I hope I mentioned it right...

No, HVM PV drivers are not included with the vanilla kernel, you need to
obtain and load them separately.


> >
> > If you're running paravirtual linux on xen, you already have
> > paravirtualized
> > ("full speed") drivers in use.
> Yes,  however, my DomU crashes on boot with the PV kernel. I couldn't find
> why.

What dom0 distribution are you using?

Are xen/kernel packages provided by the distribution or self compiled?

I'm using Ubuntu 7.10 with 2.6.22-14-xen as Dom0. Packages are provided by the distribution.  

What is your domU distribution? Is the domU PV kernel from the
distribution, or self compiled? 

DomU is Pardus 2007.2. It has default kernel 2.6.18-8, but as I wanted paravirtualization, I was using Ubuntu's 2.6.22-14-xen. The crash started with this release kernel. when Ubuntu was beta, I was able to use 2.6.22-12-xen without problems.
Pardus 2007.2 is able to work with Ubuntu 2.6.22-14-generic kernel (on bare metal) without problems. It used to be working as DomU with 2.6.22-12-xen but not anymore with 2.6.22-14-xen. I filed a bug report 1 month ago, no answer yet.

I switched to VMWare for the moment until I resolve this issue, VMWare disk performance is not good even if I enabled PV support (VMI).

Therefore, my aim now is to use standard Pardus kernel 2.6.18-8, but compile PV drivers for use with Dom0 (Ubuntu 7.10 2.6.22-14-xen, Xen 3.1)


PV domU is the most common type of virtual machine on Xen, and it definitely
works fine as long as you're running matching/compatible versions of Xen and

> >
> >
> > If you're using HVM domU on Xen, then you need to install Xen PV drivers
> > on
> > domU.
> >
> > -- Pasi
> >
> Thanks, just one last question, when I compile and modprobe these PV
> modules, how can I understand that they are actually working?   Do they
> print some message in dmesg?


Usually you need to edit/recreate your initrd to load these modules during
the domU bootup.

-- Pasi

OK, I'll do that. thanks a lot again.

Emre Erenoglu
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