Linux Virtualization - Mar 2017 - [BUG] virtio-net linux driver fails to probe on MIPS Malta since 'hw/virtio-pci: fix virtio behaviour'

Hi,

I've bisected the following failure of the virtio_net linux v4.10 driver
to probe in QEMU v2.9.0-rc1 emulating a MIPS Malta machine:

virtio_net virtio0: virtio: device uses modern interface but does not have
VIRTIO_F_VERSION_1
virtio_net: probe of virtio0 failed with error -22

To QEMU commit 9a4c0e220d8a ("hw/virtio-pci: fix virtio behaviour").

It appears that adding ",disable-modern=on,disable-legacy=off" to the
virtio-net -device makes it work again.

I presume this should really just work out of the box. Any ideas why it
isn't?

Cheers
James
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On 03/17/2017 11:57 PM, James Hogan wrote:
> Hi,
>
> I've bisected the following failure of the virtio_net linux v4.10
driver
> to probe in QEMU v2.9.0-rc1 emulating a MIPS Malta machine:
>
> virtio_net virtio0: virtio: device uses modern interface but does not have
VIRTIO_F_VERSION_1
> virtio_net: probe of virtio0 failed with error -22
>
> To QEMU commit 9a4c0e220d8a ("hw/virtio-pci: fix virtio
behaviour").
>
> It appears that adding ",disable-modern=on,disable-legacy=off" to
the
> virtio-net -device makes it work again.
>
> I presume this should really just work out of the box. Any ideas why it
> isn't?
>
Hi,


This is strange. This commit changes virtio devices from legacy to virtio
"transitional".
(your command line changes it to legacy)
Linux 4.10 supports virtio modern/transitional (as far as I know) and on QEMU
side
there is nothing new.

Michael, do you have any idea?

Thanks,
Marcel
> Cheers
> James
>

On Mon, Mar 20, 2017 at 05:21:22PM +0200, Marcel Apfelbaum
wrote:
> On 03/17/2017 11:57 PM, James Hogan wrote:
> > Hi,
> > 
> > I've bisected the following failure of the virtio_net linux v4.10
driver
> > to probe in QEMU v2.9.0-rc1 emulating a MIPS Malta machine:
> > 
> > virtio_net virtio0: virtio: device uses modern interface but does not
have VIRTIO_F_VERSION_1
> > virtio_net: probe of virtio0 failed with error -22
> > 
> > To QEMU commit 9a4c0e220d8a ("hw/virtio-pci: fix virtio
behaviour").
> > 
> > It appears that adding
",disable-modern=on,disable-legacy=off" to the
> > virtio-net -device makes it work again.
> > 
> > I presume this should really just work out of the box. Any ideas why
it
> > isn't?
> > 
> 
> Hi,
> 
> 
> This is strange. This commit changes virtio devices from legacy to virtio
"transitional".
> (your command line changes it to legacy)
> Linux 4.10 supports virtio modern/transitional (as far as I know) and on
QEMU side
> there is nothing new.
> 
> Michael, do you have any idea?
> 
> Thanks,
> Marcel
My guess would be firmware mishandling 64 bit BARs - we saw such
a case on sparc previously. As a result you are probably reading
all zeroes from features register or something like that.
Marcel, could you send a patch making the bar 32 bit?
If that helps we know what the issue is.
> > Cheers
> > James
> >