Re: [Qemu-ppc] [Qemu-devel] [QEMU PATCH v5 2/6] migration: spapr_drc: defined VMStateDescription struct

[David Gibson]

On Fri, Oct 07, 2016 at 10:17:45AM -0700, Jianjun Duan wrote:
> 
> 
> On 10/06/2016 08:12 PM, David Gibson wrote:
> > On Mon, Oct 03, 2016 at 11:24:53AM -0700, Jianjun Duan wrote:
> >> To manage hotplug/unplug of dynamic resources such as PCI cards,
> >> memory, and CPU on sPAPR guests, a firmware abstraction known as
> >> a Dynamic Resource Connector (DRC) is used to assign a particular
> >> dynamic resource to the guest, and provide an interface for the
> >> guest to manage configuration/removal of the resource associated
> >> with it.
> >>
> >> To migrate the hotplugged resources in migration, the
> >> associated DRC state need be migrated. To migrate the DRC state,
> >> we defined the VMStateDescription struct for spapr_drc to enable
> >> the transmission of spapr_drc state in migration.
> >>
> >> Not all the elements in the DRC state are migrated. Only those
> >> ones modifiable or needed by guest actions or device add/remove
> >> operation are migrated. From the perspective of device
> >> hotplugging, if we hotplug a device on the source, we need to
> >> "coldplug" it on the target. The states across two hosts for the
> >> same device are not the same. Ideally we want the states be same
> >> after migration so that the device would function as hotplugged
> >> on the target. For example we can unplug it. The minimum DRC
> >> state we need to transfer should cover all the pieces changed by
> >> hotplugging. Out of the elements of the DRC state, isolation_state,
> >> allocation_sate, and configured are involved in the DR state
> >> transition diagram from PAPR+ 2.7, 13.4. configured and signalled
> >> are needed in attaching and detaching devices. indicator_state
> >> provides users with hardware state information. These 6 elements
> >> are migrated.
> > 
> > Hmm.. are you saying that the DRC state of a coldplugged device (after
> > we've fully booted) is different from the DRC state of a hotplugged
> > device (after all the hotplug operations have fully completed)?
> > 
> > If that's correct that sounds like a general bug in the DRC state
> > management, not something only related to migration.
> > 
> > Looking at the code, though, that doesn't really seem to be what it's
> > doing.
> > 
> 
> After hotplugging a device, changes may be made to its DRC state on the
> source. But on target the state is fresh. The possible changes are shown
> in spapr_drc_needed function.

Ok.  If you can somehow include the content of the paragraph above in
your commit messages that would make the rationale clearer.

> >> detach_cb in the DRC state is a function pointer that cannot be
> >> migrated. We set it right after DRC state is migrated so that
> >> a migrated hot-unplug event could finish its work.
> >>
> >> The instance_id is used to identify objects in migration. We set
> >> instance_id of DRC using the unique index so that it is the same
> >> across migration.
> >>
> >> Signed-off-by: Jianjun Duan <address@hidden>
> >> ---
> >>  hw/ppc/spapr_drc.c         | 69 
> >> ++++++++++++++++++++++++++++++++++++++++++++++
> >>  hw/ppc/spapr_pci.c         | 22 +++++++++++++++
> >>  include/hw/ppc/spapr_drc.h |  9 ++++++
> >>  3 files changed, 100 insertions(+)
> >>
> >> diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
> >> index 6e54fd4..369ec02 100644
> >> --- a/hw/ppc/spapr_drc.c
> >> +++ b/hw/ppc/spapr_drc.c
> >> @@ -615,6 +615,71 @@ static void spapr_dr_connector_instance_init(Object 
> >> *obj)
> >>                          NULL, NULL, NULL, NULL);
> >>  }
> >>  
> >> +static bool spapr_drc_needed(void *opaque)
> >> +{
> >> +    sPAPRDRConnector *drc = (sPAPRDRConnector *)opaque;
> >> +    sPAPRDRConnectorClass *drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> >> +    bool rc = false;
> >> +    sPAPRDREntitySense value;
> >> +
> >> +    drck->entity_sense(drc, &value);
> >> +    /* If no dev is plugged in there is no need to migrate the DRC state 
> >> */
> >> +    if (value != SPAPR_DR_ENTITY_SENSE_PRESENT) {
> >> +        return false;
> >> +    }
> >> +    /*
> >> +     * If there is dev plugged in, we need to migrate the DRC state when
> >> +     * it is different from cold-plugged state
> >> +     */
> >> +    switch(drc->type) {
> >> +    /* for PCI type */
> >> +    case SPAPR_DR_CONNECTOR_TYPE_PCI:
> >> +        rc = !((drc->isolation_state == 
> >> SPAPR_DR_ISOLATION_STATE_UNISOLATED) &&
> >> +               (drc->allocation_state == 
> >> SPAPR_DR_ALLOCATION_STATE_USABLE) &&
> >> +               drc->configured && drc->signalled && 
> >> !drc->awaiting_release);
> >> +        break;
> >> +    /* for LMB type */
> >> +    case SPAPR_DR_CONNECTOR_TYPE_LMB:
> >> +        rc = !((drc->isolation_state == 
> >> SPAPR_DR_ISOLATION_STATE_ISOLATED) &&
> >> +               (drc->allocation_state == 
> >> SPAPR_DR_ALLOCATION_STATE_UNUSABLE) &&
> >> +               drc->configured && drc->signalled && 
> >> !drc->awaiting_release);
> >> +        break;
> > 
> > What about CPU type?z
> 
> For CPU Type, those states don't change from source to host.

Is that a property of the CPU type specifically, or is that just
because current guests don't mess with the CPU DRC states the way they
do with other devices?

> >> +    default:
> >> +        ;
> >> +    }
> >> +
> >> +    return rc;
> >> +}
> >> +
> >> +/* detach_cb needs be set since it is not migrated */
> >> +static void postmigrate_set_detach_cb(sPAPRDRConnector *drc,
> >> +                                      spapr_drc_detach_cb *detach_cb)
> >> +{
> >> +    drc->detach_cb = detach_cb;
> >> +}
> >> +
> >> +/* return the unique drc index as instance_id for qom interfaces*/
> >> +static int get_instance_id(DeviceState *dev)
> >> +{
> >> +    return (int)get_index(SPAPR_DR_CONNECTOR(OBJECT(dev)));
> >> +}
> >> +
> >> +static const VMStateDescription vmstate_spapr_drc = {
> >> +    .name = "spapr_drc",
> >> +    .version_id = 1,
> >> +    .minimum_version_id = 1,
> >> +    .needed = spapr_drc_needed,
> >> +    .fields  = (VMStateField []) {
> >> +        VMSTATE_UINT32(isolation_state, sPAPRDRConnector),
> >> +        VMSTATE_UINT32(allocation_state, sPAPRDRConnector),
> >> +        VMSTATE_UINT32(indicator_state, sPAPRDRConnector),
> >> +        VMSTATE_BOOL(configured, sPAPRDRConnector),
> >> +        VMSTATE_BOOL(awaiting_release, sPAPRDRConnector),
> >> +        VMSTATE_BOOL(signalled, sPAPRDRConnector),
> >> +        VMSTATE_END_OF_LIST()
> >> +    }
> >> +};
> >> +
> >>  static void spapr_dr_connector_class_init(ObjectClass *k, void *data)
> >>  {
> >>      DeviceClass *dk = DEVICE_CLASS(k);
> >> @@ -623,6 +688,8 @@ static void spapr_dr_connector_class_init(ObjectClass 
> >> *k, void *data)
> >>      dk->reset = reset;
> >>      dk->realize = realize;
> >>      dk->unrealize = unrealize;
> >> +    dk->vmsd = &vmstate_spapr_drc;
> >> +    dk->dev_get_instance_id = get_instance_id;
> >>      drck->set_isolation_state = set_isolation_state;
> >>      drck->set_indicator_state = set_indicator_state;
> >>      drck->set_allocation_state = set_allocation_state;
> >> @@ -636,6 +703,8 @@ static void spapr_dr_connector_class_init(ObjectClass 
> >> *k, void *data)
> >>      drck->detach = detach;
> >>      drck->release_pending = release_pending;
> >>      drck->set_signalled = set_signalled;
> >> +    drck->postmigrate_set_detach_cb = postmigrate_set_detach_cb;
> >> +
> >>      /*
> >>       * Reason: it crashes FIXME find and document the real reason
> >>       */
> >> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> >> index 4f00865..080471c 100644
> >> --- a/hw/ppc/spapr_pci.c
> >> +++ b/hw/ppc/spapr_pci.c
> >> @@ -1594,11 +1594,33 @@ static void spapr_pci_pre_save(void *opaque)
> >>      }
> >>  }
> >>  
> >> +/*
> >> + * detach_cb in the DRC state is a function pointer that cannot be
> >> + * migrated. We set it right after migration so that a migrated
> >> + * hot-unplug event could finish its work.
> >> + */
> >> +static void spapr_pci_set_detach_cb(PCIBus *bus, PCIDevice *pdev,
> >> +                                 void *opaque)
> >> +{
> >> +    sPAPRPHBState *sphb = opaque;
> >> +    sPAPRDRConnector *drc = spapr_phb_get_pci_drc(sphb, pdev);
> >> +    sPAPRDRConnectorClass *drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> >> +    drck->postmigrate_set_detach_cb(drc, spapr_phb_remove_pci_device_cb);
> > 
> > Why is spapr_phb_remove_pci_device_cb the right callback rather than
> > something else?  This doesn't seem sensible.
> > 
> > More to the point, you're not restoring detach_cb_opaque, which means
> > the detach_cb callback won't work properly anyway.
> > 
> If set_isolation_state/set_allocation_state is called on target without
> spapr_phb_remove_pci_device being called earlier, drc->detach_cb is
> null. Its value is spapr_phb_remove_pci_device_cb and is set in
> spapr_phb_remove_pci_device.
> 
> You are right about detach_cb. It needs be restored.

Right.

It sounds like detach_cb is doing double duty - it is pointing to what
the right detach function is, and also acting as a flag to say if a
detach operation is necessary.  This doesn't play well with migration.

In order to do sane migration, I suspect we need to split this into
different components - the callback value can maybe move to the class
instead of the DRC instance (or just use a switch on drc_type).  The
flag can just become a boolean which we can migrate.

> >> +}
> >> +
> >>  static int spapr_pci_post_load(void *opaque, int version_id)
> >>  {
> >>      sPAPRPHBState *sphb = opaque;
> >>      gpointer key, value;
> >>      int i;
> >> +    PCIBus *bus = PCI_HOST_BRIDGE(sphb)->bus;
> >> +    unsigned int bus_no = 0;
> >> +
> >> +    /* Set detach_cb for the drc unconditionally after migration */
> >> +    if (bus) {
> >> +        pci_for_each_device(bus, pci_bus_num(bus), 
> >> spapr_pci_set_detach_cb,
> >> +                            &bus_no);
> >> +    }
> >>  
> >>      for (i = 0; i < sphb->msi_devs_num; ++i) {
> >>          key = g_memdup(&sphb->msi_devs[i].key,
> >> diff --git a/include/hw/ppc/spapr_drc.h b/include/hw/ppc/spapr_drc.h
> >> index fa531d5..17589c8 100644
> >> --- a/include/hw/ppc/spapr_drc.h
> >> +++ b/include/hw/ppc/spapr_drc.h
> >> @@ -192,6 +192,15 @@ typedef struct sPAPRDRConnectorClass {
> >>                     void *detach_cb_opaque, Error **errp);
> >>      bool (*release_pending)(sPAPRDRConnector *drc);
> >>      void (*set_signalled)(sPAPRDRConnector *drc);
> >> +
> >> +    /*
> >> +     * QEMU interface for setting detach_cb after migration.
> >> +     * detach_cb in the DRC state is a function pointer that cannot be
> >> +     * migrated. We set it right after migration so that a migrated
> >> +     * hot-unplug event could finish its work.
> >> +     */
> >> +    void (*postmigrate_set_detach_cb)(sPAPRDRConnector *drc,
> >> +                                      spapr_drc_detach_cb *detach_cb);
> >>  } sPAPRDRConnectorClass;
> >>  
> >>  sPAPRDRConnector *spapr_dr_connector_new(Object *owner,
> > 
> 
> Thanks,
> Jianjun
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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