Re: [SeaBIOS] [PATCH] init_virtio_scsi(): reset the HBA before freeing its virtio ring

[Laszlo Ersek]

On 01/17/14 18:17, Kevin O'Connor wrote:
> On Wed, Jan 15, 2014 at 11:01:59AM +0100, Paolo Bonzini wrote:
> > Il 15/01/2014 02:48, Laszlo Ersek ha scritto:
> > > When init_virtio_scsi() finds no SCSI targets connected to the HBA, it
> > > frees the virtio ring. Other code in SeaBIOS proceeds to overwrite the
> > > area. However, the ring is in use by qemu at that point -- not only did we
> > > report the (ACK|DRIVER|DRIVER_OK) status earlier, we even communicated
> > > over the ring.
> > >
> > > Of course SeaBIOS doesn't "kick" the HBA ever again, hence qemu has no
> > > reason to look at the ring. However, when qemu uses KVM acceleration, and
> > > ioeventfd is enabled for the HBA, then a vmstate change to "running"
> > > (including stop->cont monitor commands and incoming migration) "forces" a
> > > kick (see qemu commit 25db9ebe). Qemu then tries to interpret whatever
> > > unrelated guest data is in the HBA's original ring area, as virtio
> > > protocol. Qemu exits upon seeing the garbage.
> > >
> > > init_virtio_scsi() should reset the HBA before allowing the virtio ring
> > > memory to be reused. Device reset causes the hypervisor to drop its
> > > references.
> > >
> > > This change is justified / underpinned by pure virtio-spec compliance as
> > > well.
> > >
> > > Related RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1013418
> > >
> > > Signed-off-by: Laszlo Ersek
>
> [...]
> > Thanks Laszlo!
> >
> > Reviewed-by: Paolo Bonzini
> >
> > Paolo
>
> Thanks Laszlo - I'm sure that wasn't easy to find.

No, it wasn't; the BZ is public and anyone can see my struggle.
> I've pushed the
> patch.

Thank you!

Laszlo