I've been having this problem on my Intel Arc A750 since trying to upgrade from 7.2.4 and it was driving me crazy. Gave it another swing today, asking ChatGPT to come up with ideas and "we" managed to fix it. Here's what it came up with (more info on my system below) : Shut down VM Edit > XML View Change the <domain> tag and add an entry before the final </domain> tag (see code below) Start VM and enjoy GPU passthrough Here's the code - At the very beginning I changed the <domain ...> tag to: <domain type='kvm' id='2' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>At the very end, just before the final </domain> tag, I added: <qemu:commandline>
<qemu:arg value='-global'/>
<qemu:arg value='pcie-root-port.mem-reserve=32M'/>
</qemu:commandline> Some more info: My configuration: Unraid 7.3.3 (upgrading from 7.2.4) Intel Arc A750 (GPU and audio passed through) Bazzite Linux Q35 9.2 with OVMF GPU assigned to a dedicated PCIe root port After upgrading, the VM would boot, but the GPU failed to initialize properly. The Bazzite kernel logs showed PCIe BAR allocation errors: BAR 0: can't claim; no compatible bridge window BAR 0: can't assign; no space BAR 0: failed to assign The GPU required a 16 MiB non-prefetchable memory region, but the PCIe root port only had a 2 MiB memory window. After restarting the VM, the GPU's BAR 0 was successfully allocated at 0x82000000, the Intel i915 driver initialized correctly, and the GPU firmware loaded successfully. The initial can't claim message still appears, but Linux subsequently reallocates the BAR successfully. The can't assign; no space and failed to assign errors are gone. Everything appears to be working normally now, including GPU initialization, while retaining Q35.