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Re: [Xen-users] Xen VGA Passthrough - GTX 480 successfully quadrified to quadro 6000 (softmod) - more than 4GB of RAM for Win XP 64 Bits

On 09/23/2013 07:33 PM, David TECHER wrote:
FYI I didn't try your patch for the moment.

My patch is _only_ needed on broken hardware where the DMA bypasses the IOMMU, e.g. with NF200 PCIe bridges, and while it is possible that other hardware is affected by similar bugs, I have not heard reports to that effect.

And for the record, the irony is not lost on me of Nvidia NF200 bridges thoroughly breaking virtualization while Nvidia GPUs being the only fit-for-purpose option for VGA passthrough.

I noticed the slowdown when setting RAM > 3GB in configuration file. I
did the test on a old and fresh current VM XP64.

Can you explain what do you mean by slowdown? I'm wondering if this is in some way related to memory hole remapping.

Yesterday I set up a new VM XP 64 from scratch. Once NVIDIA driver was
installed I restarted the VM. Extremely slow if RAM > 3GB.

Just out of interest - what do you get from:
lspci -vvv | grep "Region " | grep "Memory at " | sed -e 's/.*Memory at //' | sort

Can you check if the slowdown begins when you assign the amount of memory to the domU that begins to exceed the address at the first line of that command?

So I set RAM <= 3GB VM worked pretty fine

Perhaps I may have a try for your patch and let you know.

The last patch (WORK IN PROGRESS!) I posted was specific to my setup, and IIRC it essentially marks everything above 1GB as a memory hole, but it didn't adjust the top end of the memory, so you effectively lose 2.5GB of RAM you allocate to the domU. By all means try it, just bear in mind it is not for for general consumption.


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