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Re: [Xen-users] VGA Passthrough of AMD HD8670D IGP to HVM Win7 results in "Code 43"

I wasn't aware that there was a restriction
regarding the DomU RAM. However, it just so
happens that I always tried with "memory=2048".

So far so good.

I assume this satisfies the <= 2GB RAM
requirement, although I'm not sure since I
don't know whether you refer to "base-10 G"
or "base-2 G". :)

Base 2. Perhaps I should have said 2GiB. :)

Furthermore, I don't know whether the setting
"shadow_memory = 512" counts towards that

What does that do?

or whether the 1024MB that has been assigned
to the integrated GPU in BIOS does.

Your GPU has a 1GB BAR? Really? I don't think
I've ever seen GPU BARs > 256MB. That could
potentially shrink the amount of RAM you
can reliably give the domU. Try with

Note: This should be fixed in 4.3, but I haven't
tried it yet.

Yes, I have tried without any first party
patches, as I had written in my first mail in
this thread. However, I haven't tried
"unpatched" xen with kernel 3.8.13 yet - should I?

I got this working with 4.2.2 + XSA patches
(mainly because that is what is in the RPMs I
use, I'm on EL6).

Unfortunately, I don't have a spare dedicated
graphics card I could add right now. I will try
to get one (is it important whether it's PCI or
PCIe, nVidia or ATI, or some specific model?)
and report back (if) when I get hold of one.

There is no particular requirement but it will
make it simpler if you have a dom0 card that
doesn't use the same drivers as the domU cards.
Otherwise, if you have xen-pciback as a module
you have to do some extra configuration/scripting
to ensure that upon loading the GPU driver, the
xen-pciback gets assigned the GPUs you don't want
the dom0 driver to handle. My setup is like this
at the moment and it works fine, but to make my
life easier I am going to switch to using
an old ATI 4850 (best I can get ATI-wise that is
single-slot and has two DL-DVI ports) for dom0,
and a pair of GeForce GTX480 modified into
Quadro 6000s for two separate domUs. I'm
currently using a GeForce 8800GT for dom0,
which is what I'll be replacing with a HD4850
in the near future (i.e. when I get around to
acquiring one).

However, my primary goal was to build a
computer that would serve two independent VMs
with 3D acceleration each, e.g. so that two
people could play games at the same time.

This is _precisely_ my use case, with the
extra requirement of also being my primary
workstation at the same time (without that
purpose having to be interrupted for gaming

My plan was to buy the hardware as I have it
right now, test whether I could make xen
pass-through the one (integrated) GPU I have
right now,

Oh, is THIS what you were referring to by
1GiB for the GPU? That's not the same as BARs,
disregard what I said above.

and then buy a not-too-expensive
but still quite powerful dedicated GPU.
I would be much happier if I didn't have
to buy and install a third GPU, although
I realize me wishing that doesn't necessarily
make it so. ;)

My general experience is that integrated GPUs
aren't really up to gaming requirements in the
majority of cases, so my advice would be to get
a pair of different GPUs for VGA passthrough
and stick with the integrated one for dom0.

My experience with ATI for VGA passthrough has
been somewhat poor, but provided you avoid
PCI memory stomps and weird IRQ clash issues,
the experience with Nvidia Quadros has been
very positive. GeForce cards won't work
until/unless you modify them into equivalent
Quadros. See:

One thing that ATI users seem to be experiencing
is progressive graphics slow-down after reboots
in domUs with VGA passthrough, which requires
host reboot to fix. I have not experienced this
with my Quadrified GeForce cards.

It took a lot of effort to get this working and
work around all the issues, though. Which slots
you have the hardware in makes a difference, as
does the nature and number of PCIe bridges
involved, as well as the combination of hardware
you are passing through. ACS support on the
PCIe bridges may also help ensure that a bug
causing a PCI memory stomp doesn't crash dom0,
although I have managed to get things working
stably and reliably without it.


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