Re: Passthrough of 2 PCI devices works 80% (Kernel 2.6.37, Debian Squeeze, Win7 VM)

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 2011-02-15 at 20:57 +0000, Da Powah wrote:
> Hi,
> 
> i`ve got a question about pci passthrogh of 2 pci devices (2x DVB-S2
> PCI cards with Saa7146 PCI Bridge from Technotrend: S2-3200). 
> 
> I am using squeeze with a 2.6.37 selfcompiled Kernel. I want to
> passthrough both devices to a virtual machine (Win7) an get problems.
> If i passthrough one device (other is unplugged) it works flawlessly. 

I'm glad to hear it works one at a time.  It's oddly specific that you
mention it works if the other card is unplugged, can you only physically
have one card plugged in at a time for it to work (ie. if you have both
cards physically installed, but only one assigned to the guest, does it
work)?  Can you simultaneously assign each card to separate guests and
they work?

> The time i add both devices and pass them through i am still able to
> start the VM and i don`t see anything in the error logs. Even Windows7
> or XP detects both cards and installs the driver correctly (actual BDA
> Driver, standard broadcast video driver). But the time i want to acces
> the cards, i get a BSOD - caused by the driver.

I'll toss out a dumb question, can the drivers for Win7 or WinXP drive
two cards when running on bare metal?  Does a Linux guest work with both
cards better?

> I already aligned the io memory of both devices, checked the libvirt
> logs, kernel and syslogs - there is nothing for a kvm newbe that seems
> to be odd. The kernel is compiled with all the mentioned kernel
> options of the linux-kvm.org page - except that i compiled the stub
> driver as module. One card alone (both tried separately) is working
> w/o any flaws. Kvm is able to pass through all devices behind a PCI
> Bridge - so take a look at the 03:0x.0 devices below: i use those 2
> sat boards only in 3 PCI slots.
> 
> What am i able to do to make deeper analysis or to solve the
> problem ? 

If each card works when assigned separately and you can boot the guest
with both cards assign and the drivers load and device manager isn't
reporting any errors, I'd lean towards a Windows driver issue.  There is
some debugging you can enable in hw/device-assignment.c that might shed
some light on what the drivers is trying to do before the BSOD.  What
error is the BSOD reporting?  Are you using the latest qemu-kvm.git?
Thanks,

Alex