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[Qemu-devel] Nested PCI passthrough

From: fassl
Subject: [Qemu-devel] Nested PCI passthrough
Date: Sat, 21 Jan 2017 04:16:25 +0100


i am trying to pass through a graphic card to a guest within a guest.
So far i can see a text console within the target vm which says
"radeon: ring 0 test failed", so it times out in radeon_vce_ring_test
function. I am using qemu 2.8.50 at revision

The relevant lowermost host arguments are:
-machine pc-q35-2.8,accel=kvm,kernel-irqchip=split
-device intel-iommu,intremap=on,eim=on

If i dont set the x-vga flag for the passed through device in the
lowermost host the VM within the VM does not reset(?) the device during
shutdown and the screen freezes. If i do, the screen goes black and no
signal is going to the screen anymore and i can restart the target VM
without the whole machine freezing. (one has to set
CONFIG_VFIO_PCI_VGA=y in the kernel of the first VM, or call
pci_register_vga to get this)

Also with irqchip=split the first vm cannot shutdown gracefully and
crashes during shutdown.

I also can see some IRTE vector and trigger mode inconsistencies, can
they cause this?

Or are there some quirks to be done to get this going?

If anybody could lead me into the right direction or if there is work
going on in this field i would be more than glad to help testing.

Thank you in advance

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