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Re: [Xen-users] New to Xen: safety concerns (Linux Dom0, Windows DomU)

On Friday, September 09, 2011 2:05 PM, "Chris Angelico" <rosuav@xxxxxxxxx> 
> I assume I can switch it to a different VM on the fly? That is, boot
> with the graphics card dedicated to dom0 Linux, then fire up domU
> Windows and hand control over.

I've successfully done Debian-to-Debian handover of a Radeon card on my machine,
but it's not like a KVM---it's considerably more involved than that, involving
poking various low-level Linux bits on the dom0 before hitting the xm pci-attach
button (so to speak), and involving some workarounds regarding PCI interrupts (I
had to use pci=nomsi in the domU, but maybe that's not needed in the long run;
I'm still experimenting during my Copious Free Time).  There may be easier tools
available than what I'm using, but if so I don't know what they are.  Also I'm 
passthrough to secondary slot rather than to primary, so the domU BIOS and 
console are on the emulated Cirrus VGA.

> http://ubuntuforums.org/archive/index.php/t-953793.html - required
> some manual cleanup and not sure if it really cleaned up (dated 2008)

The latter looks like ey's just trying to clean away extra directories, no?
That sounds non-critical.  (I'm guessing ey's also not heard of aptitude purge.)

> Not enough weight of evidence to turn me away from Xen, but enough to
> be concerned about.
> According to `uname -a` it's currently 2.6.35-30-generic. I could
> upgrade the kernel to version 3 I guess, but I'm not a kernel expert
> so I'd be navigating unfamiliar waters. It'd be a separate "can I undo
> this if things go wrong" question all of its own.

I'm curious why you don't just make a bitwise copy of the entire hard drive
(or other primary storage) before doing anything.  That would be a bit 
and require extra hardware, but it would seem to leave the least room for 
stuck positions later on while being very straightforward to start with.

> Thank you. I believe you, for I am sure you would not practice on my
> inexperience.

I'm not particularly a Xen master either, mind you, but I've installed and 
it on a server box before and the relative difficulty of flipping either way 
was just
picking the right GRUB entry and aptitude install/purge.  This was a few years 
though, and I didn't set up anything too extensive on it.

> I want to play graphical Windows games. It's a 64-bit system with 8GB
> of RAM and a fairly new nVidia chipset video card (don't remember the
> spec atm), so in theory I should be able to give 2-3GB to a 32-bit
> WinXP and let that run happily, while leaving 5-6GB of real RAM for
> everything else.

Maybe.  I'm not sure how much I'd trust the combination of passed-through 
nVidia card
and virtual PCI bridge with Windows gaming drivers; I thought those were often 
likely to use dirty tricks that might not play well with such an idiosyncratic 
setup?  I have very little contact with Windows these days.

> Hmm. Is there an easy way to check? It's a high-end Intel motherboard,
> and a high-end modern CPU, although I don't have the precise
> identifiers to hand.

I purchased my hardware specifically targeting having VT-d (Intel IOMMU) 
you might look at http://wiki.xensource.com/xenwiki/VTdHowTo and see whether it
sparks anything.  On my mainboard (an Asus P8B WS server/workstation-class 
I had to specifically update the BIOS to the latest mid-2011 version and then 
the VT-d feature.

> I'm not afraid of a bit of complexity, but my areas of expertise are
> user-level (ring 3) software and networking, not kernels and
> hypervisors. Much appreciate your help!

Simplicity is good.  Features are also good.  But backups are the best.  :-)

> Chris Angelico

   ---> Drake Wilson

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