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


From: Gal Hammer
Subject: [Qemu-devel] MSI-X doesn't work when running Windows as guest
Date: Thu, 12 Sep 2013 11:23:46 +0300
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130801 Thunderbird/17.0.8

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.



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