RE: [Xen-users] gaming in a windows domU?

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Igor Chubin
> Sent: 13 April 2007 10:29
> To: Andrew Yates
> Cc: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] gaming in a windows domU?
> 
> On Do, Apr 12, 2007 at 05:34:29 -0400, Andrew Yates wrote:
> > I've been considering buying a second video and sound card, and then
> > using PCI passthrough with a Windows domU for gaming.
> > Has anyone tried this? I'm curious as to whether it's fast 
> enough for
> > recent games to be playable. The video card and CPU can 
> handle gaming
> > fine, but I'm not sure how much Xen would effect that. So has anyone
> > done this? How well did it work?
> > 
> 
> Do HVM domain support PCI passthrough?

No. But that's the EASY part to solve. The hard part is that the HVM OS
isn't aware that what it thinks is a physical address is in fact not
really the address that the memory controller is accessing when the
software accesses a virtual address. 

If we simplify things[1] to make it easy to explain: Dom0 uses 0..256MB,
HVM DomU uses 256..512MB, but thinks it got memory from 0..256MB. DomU
tells the hardware that there is some data at 0x100000 (1MB), but we
should really add 256MB to that address. So the hardware will use
something that lives at 1MB in the Dom0 instead. Most likely, this will
just lead to complete garbage being sent to the hardware, which isn't so
bad. If it happens to be something that actually works with the hardware
it may send your list of passwords to a random address on the internet
or some such!

[1] In reality, each 4KB of guest memory could come from any 4K section
of the machines memory, so it's not as simple as just adding an offset -
but that's just a slight complication on top of the fact that DomU
doesn't actually know that it's memory isn't where it thinks it is. 

--
Mats
> 
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> -- 
> WBR, i.m.chubin
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