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Re: [Xen-users] Uninitialized hardware under Xen Client?

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Uninitialized hardware under Xen Client?
From: Andy Burns <lists.xensource.com@xxxxxxxxxxxxxx>
Date: Sun, 06 Jul 2008 10:37:53 +0100
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On 06/07/2008 09:59, Kenneth Andresen wrote:

I have been trying quite hard today to get the Xen working with some of
my live cd's to test the PCI, but so far without any luck;

It can be bit of a headache, while I have managed to get my TV tuner
card almost working, the domU has a tendency to panic with one set of
settings or the hardware doesn't function properly with another set of
settings (the swiotlb I was talking about)

I am
considering if my problems steam from having an Intel Quad Core rather
than AMD, and trying to run it using HVM rather than para-virtual.

My machine is an intel quad core, so you're OK on that front, but if
your domU is HVM, then for PCI passthrough I believe you need to have
intel VT-d (as well as VT-i) support in hardware and xen. I gather this
should be supported by Q35/P45/X48 boards with chipsets and *might* be
supported by some boards with X38 chipsets.

Are you interested in windows domU as well as linux domU?

I have tried to use the virt-manager to create an initial xen install,

virt-manager uses libvirt's XML config files, which don't have a way to
add pci passthrough, you need the xmdomain.cfg format files.

name = "InsideSecurity"
memory = 512
root = "/dev/hdc ro"
#root = "/dev/ram0 rw"
kernel = "/root/isolinux/vmlinuz"
#ramdisk = "/root/isolinux/miniroot.lz"
vcpus = 1
vif = [ 'mac=00:01:01:01:01:01' ]
disk = [ "file:/boot/iso/INSERT-1.3.9b_en.iso,hdc,r" ]
pci = ['07:03.0']

that's the right format

However this fails with an the following error message:

Error: (2, 'Invalid kernel', 'xc_dom_find_loader: no loader found\n')

I've only used xen "the other way" with pygrub as the bootloader, so
that the kernel is inside /dev/hdc and is extracted by the bootloader at
boot time, for xen to initialise the domU.

While searching for information about my problems, I have come across
that it is generally seen as better to use Para virtualization rather
than hardware. Can para virtual work with unmodified linux client
kernels or default pfSense (BSD based), or will I have to use HVM for this?

paravirt will probably get you better performance, but the domU kernel
has to know that it is running under xen (it can either be a specific
kernel built for xen, or a paravirt_ops kernel that can decide at boot
time whether it is on xen, or bare-metal)

with HVM the kernel believes it is running on bare-metal when it isn't
and xen/qemu provide the smoke and mirrors.

Will HVM work as intended with Intel Quad Core cpu the default
Redhat/Centos 5.2 kernel (kernel-xen-2.6.18-92.1.6.el5.x86_64) and Xen
3.0.4 with their respective patches, or will I need to use modified
kernel / upgraded Xen version to 3.2?

you'll need the kernel-xen as the dom0, I'd be tempted to also use
kernel-xen for the domU (paravirt) but you can also use normal
kernel-2.6 for the domU (HVM) but I doubt you'll get PCI passthrough.

there is a third way, redhat recently release paravirt drivers for HVM
kernels, not tried them though and I don't think they're "in" centos yet.




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