Re: [Qemu-devel] dataplane bug: fail to start Windows VM with dataplane enable

[Stefan Hajnoczi]

On Wed, Mar 27, 2013 at 02:32:19PM +0100, Stefan Hajnoczi wrote:
> On Tue, Mar 26, 2013 at 11:10:35PM +0800, 张磊强 wrote:
> > Hi,  Paolo && Stefan:
> > 
> > When I test the dataplane feature with qemu master, I find that
> > Windows (Windows 7 and Windows 2003) VM will hang if dataplane is
> > enabled. But if I try to start a Fedora VM, it can start normally.
> > 
> > The command I boot QEMU is:
> > x86_64-softmmu/qemu-system-x86_64 -enable-kvm -m 1024 -smp 2 -drive
> > file=win7.img,if=none,id=drive-virtio-disk,format=raw,cache=none,aio=native
> > -device 
> > virtio-blk-pci,config-wce=off,scsi=off,x-data-plane=on,drive=drive-virtio-disk,id=virtio-disk
> > 
> > I found the similar bug has reported some days ago:
> > http://lists.nongnu.org/archive/html/qemu-devel/2013-03/msg02200.html
> > . And a patch for this bug has already committed by Paolo at Mar 13:
> > http://lists.nongnu.org/archive/html/qemu-devel/2013-03/msg02200.html
> > .
> > 
> > But it cannot work under my environment. Could you give me some advise
> > to debug this problem ? I can provide more information if need.
> 
> Hi,
> I haven't gotten to the bottom of it yet but wanted to let you know that
> I'm seeing a hang at the boot screen after the installer reboots.  The
> Windows logo animation runs but the guest seems unable to make progress.
> 
> Will let you know when there is a fix.  The guest I'm testing is Windows
> 7 Professional 64-bit.
> 
> As a workaround you can set x-data-plane=off to boot the guest for the
> first time.  Subsequent boots will succeed with x-data-plane=on.

Next data point, it's not caused by the Paolo's AioContext conversion.
This means it's unrelated to the recent bug that you mentioned.

The boot gets stuck immediately after the switch from the BIOS
virtio-blk driver to the Windows viostor driver.  We get two requests
(VIRTIO_BLK_T_GET_ID and VIRTIO_BLK_T_READ) and then the guest stops.
The descriptor index of the second request has been incremented, perhaps
the guest is not receiving host->guest notifies.

Stefan