Re: [Qemu-discuss] vga passthrough good on winXP 32bit but not win7 64bit

[Jakob Bohm]

On 9/26/2012 4:01 PM, lejeczek wrote:
> hi everybody
>
> this is my first fiddling with passing through hardware to a guest 
> thus what follows may sound lame, apologies.
>
> OS is rhel 6.3 64bit on a Dell poweredge box
> two different VGAs, geforce 640 and radeon hd5450
Which one do you pass through?
> guests are XP 32bit and 7 64bit
>
> should be simple right?
>
> XP seems to reports everything OK, I reckon sort of an ultimate 
> confirmation is that I get the guest on the external screen
>
> 7 always! (regardless which VGA, different PCI slot also tried, tried 
> with different command line params) reports the device marked with 
> exclamation as non-running
>
> I'm at loss for ideas of how to troubleshoot it further
Maybe the ATI or NVidia driver for the passed through card accesses
additional registers in the Windows 7 version of those drivers compared
to the XP version of those drivers.

My initial guess would be the PCI configuration space registers, but it
could be any other registers or memory you forgot to pass through.

Another possibility is that the passed through card has "internal"
knowledge about the physical address of some of the passed through
registers or memory, and the Windows 7 driver doesn't like that the
simulated physical addresses where those are passed through do not
match the physical reality reported by the card.  If at all possible, I
suggest that complex adapters (such as graphics card) are passed through
with exactly the same "physical" addresses in the virtual machine as in
the real physical machine.

Also, for extreme bus master PCI cards such as graphics cards, it is
very important to use a CPU and/or chipset which intercepts all
requests from the graphics hardware to the rest of the computer (such
as DRAM and/or other cards) and lets qemu map those exactly the same
way as those addresses are mapped for the CPU.  For Intel CPUs, this is
called VT-d, for most other brands (AMD, IBM 360) it is called IOMMU.
> help?
>
> regards

Enjoy

Jakob
--
Jakob Bohm, CIO, Partner, WiseMo A/S. http://www.wisemo.com
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