[Qemu-discuss] QEMU PCI Passthrough FPGA with more than 2GB never starts

[Miltos Hatzimihail]

Dear All

I ve got a system with a Xilinx FPGA on a PCI express slot and I am trying to 
pass it through using QEMU with vfio-pci. Here’s my command line:

qemu-system-x86_64 -smp 4,sockets=2,cores=1,threads=2 -machine 
pc-i440fx-xenial,accel=kvm  --cpu qemu64 -enable-kvm -vnc :1   -device 
vfio-pci,host=04:01.0 .. .. .. -mem 2G

The VM starts OK with men = 2G. If I try to assign more memory to this host 
(say 4GB), then the VM doesn’t even boot to the BIOS (it says that ‘This guest 
has initialised the display ‘yet’). The weird thing is that if I omit the 
passthrough, the VM starts ok with 4GB.

The PCI device is configured as follows:

        Region 0: Memory at c1100000 (32-bit, non-prefetchable) [disabled] 
[size=128K]
        Region 1: Memory at c0000000 (32-bit, non-prefetchable) [disabled] 
[size=16M]
        Region 2: Memory at 80000000 (32-bit, non-prefetchable) [disabled] 
[size=1G]
        [virtual] Expansion ROM at c1000000 [disabled] [size=1M]

I tried to find an answer online but I had no luck. What am I missing?

Regards,
Milton