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

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Sep 12, 2013 at 11:23:46AM +0300, Gal Hammer wrote:
> 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.


So it's a known change from qemu-kvm to qemu.
With qemu-kvm the default cpu was kvm64.
With qemu the default cpu is qemu64 even if you use -enable-kvm.

Not an issue for libvirt as that specifies -cpu,
but will be an issue for command-line users.

Maybe we should change the default for new machine types and when
-enable-kvm is specified?

Eduardo?
Anthony?

-- 
MST