Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 26 Sep 2017 20:40:25 +0200
David Hildenbrand <david@redhat.com> wrote:

> On 26.09.2017 18:20, Cornelia Huck wrote:
> > d32bd032d8 ("s390x/ccw: create s390 phb conditionally") made
> > creating the s390 phb dependant on the zpci facility. This broke
> > migration from pre-cpu model machines which was fixed with
> > 8ad9087c4a ("s390x/ccw: create s390 phb for compat reasons as well").
> > However, that is not enough: Migration from 2.10 with -cpu z13
> > breaks as well.
> > 
> > Let's create a phb for all pre-2.11 compat machines to fix this.
> > We leave the zpci facility off to avoid a guest-visible change
> > with cpu models on.
> > 
> > Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
> > Fixes: d32bd032d8 ("s390x/ccw: create s390 phb conditionally")
> > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> > ---
> >  hw/s390x/s390-virtio-ccw.c         | 8 +++++++-
> >  include/hw/s390x/s390-virtio-ccw.h | 1 +
> >  2 files changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> > index 1bcb7000ab..981f1c4336 100644
> > --- a/hw/s390x/s390-virtio-ccw.c
> > +++ b/hw/s390x/s390-virtio-ccw.c
> > @@ -247,6 +247,8 @@ static void s390_create_virtio_net(BusState *bus, const char *name)
> >      }
> >  }
> >  
> > +static S390CcwMachineClass *get_machine_class(void);
> > +
> >  static void ccw_init(MachineState *machine)
> >  {
> >      int ret;
> > @@ -266,7 +268,7 @@ static void ccw_init(MachineState *machine)
> >                        machine->initrd_filename, "s390-ccw.img",
> >                        "s390-netboot.img", true);
> >  
> > -    if (s390_has_feat(S390_FEAT_ZPCI)) {
> > +    if (s390_has_feat(S390_FEAT_ZPCI) || get_machine_class()->phb_compat) {
> >          DeviceState *dev = qdev_create(NULL, TYPE_S390_PCI_HOST_BRIDGE);
> >          object_property_add_child(qdev_get_machine(),
> >                                    TYPE_S390_PCI_HOST_BRIDGE,
> > @@ -407,6 +409,7 @@ static void ccw_machine_class_init(ObjectClass *oc, void *data)
> >      s390mc->cpu_model_allowed = true;
> >      s390mc->css_migration_enabled = true;
> >      s390mc->gs_allowed = true;
> > +    s390mc->phb_compat = false;
> >      mc->init = ccw_init;
> >      mc->reset = s390_machine_reset;
> >      mc->hot_add_cpu = s390_hot_add_cpu;
> > @@ -716,6 +719,9 @@ static void ccw_machine_2_10_instance_options(MachineState *machine)
> >  
> >  static void ccw_machine_2_10_class_options(MachineClass *mc)
> >  {
> > +    S390CcwMachineClass *s390mc = S390_MACHINE_CLASS(mc);
> > +
> > +    s390mc->phb_compat = pci_available;
> >      ccw_machine_2_11_class_options(mc);
> >      SET_MACHINE_COMPAT(mc, CCW_COMPAT_2_10);
> >  }
> > diff --git a/include/hw/s390x/s390-virtio-ccw.h b/include/hw/s390x/s390-virtio-ccw.h
> > index a9a90c2022..fb717afe92 100644
> > --- a/include/hw/s390x/s390-virtio-ccw.h
> > +++ b/include/hw/s390x/s390-virtio-ccw.h
> > @@ -41,6 +41,7 @@ typedef struct S390CcwMachineClass {
> >      bool cpu_model_allowed;
> >      bool css_migration_enabled;
> >      bool gs_allowed;
> > +    bool phb_compat;
> >  } S390CcwMachineClass;
> >  
> >  /* runtime-instrumentation allowed by the machine */
> >   
> 
> I'd really really really (did I mention really?) favor something like a
> dummy device, because we could easily handle the !CONFIG_PCI case then.
> 
> All these compat options and conditions will kill us someday... we're
> already patching around that whole stuff way too much.
> 
> If we ever unconditionally created a device, we should keep doing so.

Yes, that whole thing is horrible, especially interaction with compat
machines.

Do you have an idea on how to create such a dummy device (without
having to effectively copy a lot of configured-out code)?