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

From: lejeczek
Subject: Re: [Qemu-discuss] vga passthrough good on winXP 32bit but not win7 64bit
Date: Thu, 27 Sep 2012 09:21:52 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120827 Thunderbird/15.0

also, guests here with VGA passed though never restart/reboot, a restart from within the guest does power-down the guest (probably wrongly/incompletely passed VGA?? as Jakob says) and as I understand it there always be two VGAs in the guest, quemu's own and the passed one, right?


On 27/09/12 09:01, lejeczek wrote:
I was trying both VGAs alternately, while one was passed through the other was out of the box, and the box, hardware, itself is one the latest Dell poweredge servers so yes, IOMMU when I'm back in the office I'm going to double check the XP that worked

but in the meanwhile, is there any detailed help page where one can read about passing though all these registers and addresses, eexamples maybe? apart from the code which I can't read, I ain't a programmer I've been searching the web but nothing could find, discouraging.

thanks Jakob for your help

On 26/09/12 16:36, Jakob Bohm wrote:
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.





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