[Qemu-devel] MSI-X doesn't work when running Windows as guest

[Gal Hammer <ghammer@redhat.com>]

Hi,

I've notice that the virtio-serial Windows' driver doesn't use MSI-X 
vectors when running using upstream qemu or 
qemu-kvm-1.2.2-13.fc18.x86_64. The same VM works with MSI-X when using 
qemu-kvm-0.12.1.2-2.355.el6.x86_64.

 From what I saw, Windows is trying to enable MSI-X by writing a 2 bytes 
value to device's PCI-config address 66h.

So when everything works well the flow goes like this:

pci_default_write_config value: 8000 len: 2
pci_default_write_config value: 1 len: 2
msix_enabled 0 (67)
pci_default_write_config value: e107 len: 2
pci_default_write_config value: 1 len: 2
msix_enabled 0 (67)
pci_default_write_config value: 8001 len: 2
msix_enabled 1 (67)

But on upstream it goes:

pci_default_write_config addr: 66 value: 8000 size: 2
pci_default_write_config addr: 66 value: 1 size: 2
msix_enabled 0 (67)
pci_default_write_config addr: 66 value: e307 size: 2 (NOTE: Value is 
diffrent!).
pci_default_write_config addr: 66 value: 1 size: 2
msix_enabled 0 (67)

(NOTE: Missing the write of 8001).

My qemu's command line:

---< snip >---

/usr/bin/qemu-kvm -m 1G -smp 2 -enable-kvm -usb -device usb-tablet \
         -device 
ide-drive,drive=drive-virtio0-0-0,id=virtio0-0-0,bootindex=1 \
         -drive 
file=win7_32_viorng.qcow2,if=none,id=drive-virtio0-0-0,format=qcow2,werror=stop,rerror=stop,cache=none 
\
         -monitor stdio \
         -vga qxl -spice id=on,disable-ticketing,port=5903 \
         -device virtio-serial-pci,id=virtio-serial0,vectors=2 \
         -chardev spicevmc,id=spicechannel0,name=vdagent

---< snip >---

Thanks,

     Gal.