RE: [Xen-users] Windows XP, Drivers & Xen

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

> -----Original Message-----
> From: Jens Gassmann [mailto:jens.gassmann@xxxxxxxxx] 
> Sent: 04 July 2006 20:57
> To: Petersson, Mats; xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] Windows XP, Drivers & Xen
> 
> Hi Mats,
> 
> > If you want the longer answer, please look for "3D Graphics" in the
> > archives of this mailing list, as I've written the answer at least 6
> > times by now... 
> 
> I read your new FAQ item. Now i think about the use of two graphics 
> cards. Most of the new boards come with two PCI-E Slots.
> 
> Card 1 Memory Area 0 - 256M
> Card 2 Memory Area 256 - 512M
> 
> The main Dom0 use only the memory area from 0 - 256MB. The 
> DomU use the 
> memory area above the 256MB and could access the second graphic card.
> 
> Under HVM / Windows i disable the second card, and the first under 
> windows one use the memory from the second from the pci.

No, that's not how it works - all PCI[e] (and AGP, which is just a
PCI-bus on steroids) slots are able to access all memory in the system,
and they need to be told exactly which physical address - a physical
address that we've lied to the OS about, so the OS doesn't actually know
the REAL physical address... 

What you describe is an IOMMU implementation, where the address
generated by the card is translated to another physical address. But we
have yet to see (desktop) machines with IOMMU implemented in them. 

> 
> If this possible? Today two cards are cheap. Maybe we could 
> simple patch 
> the main System to reroute the access?

Yeah, right - you go wire the hardware different ;-)

--
Mats
> 
> Regards,
> Jens
> 
> 



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