Re: [Qemu-devel] [PATCH for-4.0 v4 2/2] virtio: Provide version-specific variants of virtio PCI devices

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 3 Jan 2019 11:14:44 +0100
Thomas Huth <thuth@redhat.com> wrote:

> On 2019-01-03 10:38, Thomas Huth wrote:
> > On 2018-12-05 20:57, Eduardo Habkost wrote:  
> >> Many of the current virtio-*-pci device types actually represent
> >> 3 different types of devices:
> >> * virtio 1.0 non-transitional devices
> >> * virtio 1.0 transitional devices
> >> * virtio 0.9 ("legacy device" in virtio 1.0 terminology)
> >>
> >> That would be just an annoyance if it didn't break our device/bus
> >> compatibility QMP interfaces.  With these multi-purpose device
> >> types, there's no way to tell management software that
> >> transitional devices and legacy devices require a Conventional
> >> PCI bus.
> >>
> >> The multi-purpose device types would also prevent us from telling
> >> management software what's the PCI vendor/device ID for them,
> >> because their PCI IDs change at runtime depending on the bus
> >> where they were plugged.
> >>
> >> This patch adds separate device types for each of those virtio
> >> device flavors:
> >>
> >> - virtio-*-pci: the existing multi-purpose device types
> >>   - Configurable using `disable-legacy` and `disable-modern`
> >>     properties
> >>   - Legacy driver support is automatically enabled/disabled
> >>     depending on the bus where it is plugged
> >>   - Supports Conventional PCI and PCI Express buses
> >>     (but Conventional PCI is incompatible with
> >>     disable-legacy=off)
> >>   - Changes PCI vendor/device IDs at runtime
> >> - virtio-*-pci-transitional: virtio-1.0 device supporting legacy drivers
> >>   - Supports Conventional PCI buses only, because
> >>     it has a PIO BAR
> >> - virtio-*-pci-non-transitional: modern-only
> >>   - Supports both Conventional PCI and PCI Express buses
> >>
> >> The existing TYPE_* macros for these types will point to an
> >> abstract base type, so existing casts in the code will keep
> >> working for all variants.
> >>
> >> A simple test script (tests/acceptance/virtio_version.py) is
> >> included, to check if the new device types are equivalent to
> >> using the `disable-legacy` and `disable-modern` options.
> >>
> >> Acked-by: Andrea Bolognani <abologna@redhat.com>
> >> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> >> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>  
> > 
> >  Hi Eduardo,
> > 
> > with these new devices, I can trigger an abort on s390x:
> > 
> > $ qemu-system-s390x -M s390-ccw-virtio-2.5 -monitor stdio -no-shutdown
> > QEMU 3.1.50 monitor - type 'help' for more information
> > (qemu) device_add vhost-scsi-pci-non-transitional
> > qemu-system-s390x: hw/core/qdev-properties.c:1236:
> > qdev_prop_set_globals: Assertion `prop->user_provided' failed.
> > Aborted (core dumped)  
> FWIW, it happens with x86, too:
> 
> $ qemu-system-x86_64 -M pc-i440fx-2.6 -monitor stdio
> QEMU 3.1.50 monitor - type 'help' for more information
> (qemu) device_add vhost-scsi-pci-non-transitional
> qemu-system-x86_64: hw/core/qdev-properties.c:1236:
> qdev_prop_set_globals: Assertion `prop->user_provided' failed.
> Aborted (core dumped)
> 
> Only machine types newer than 2.7 seem to be OK.

It also fails for vhost-scsi-pci-transitional on 2.6 and older machines.

The problem is that HW_COMPAT_2_6 tries to set the disable_modern
property, which the version-specific variants of virtio-pci do not have.

Not sure how to fix this. The version-specific devices cannot really
work on the compat machine.