Re: [Qemu-devel] [PATCH] pcie-root-port: let it has higher migrate priority

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Michael S. Tsirkin (mst@redhat.com) wrote:
> On Thu, Feb 01, 2018 at 02:24:15PM +0200, Marcel Apfelbaum wrote:
> > Hi Peter,
> > 
> > On 01/02/2018 13:20, Peter Xu wrote:
> > > In the past, we prioritized IOMMU migration so that we have such a
> > > priority order:
> > > 
> > >     IOMMU > PCI Devices
> > > 
> > > When migrating a guest with both vIOMMU and pcie-root-port, we'll always
> > > migrate vIOMMU first, since pcie-root-port will be seen to have the same
> > > priority of general PCI devices.
> > > 
> > > That's problematic.
> > > 
> > > The thing is that PCI bus number information is stored in the root port,
> > > and that is needed by vIOMMU during post_load(), e.g., to figure out
> > > context entry for a device.  If we don't have correct bus numbers for
> > > devices, we won't be able to recover device state of the DMAR memory
> > > regions, and things will be messed up.
> > > 
> > > So let's boost the PCIe root ports to be even with higher priority:
> > > 
> > >    PCIe Root Port > IOMMU > PCI Devices
> > > 
> > > A smoke test shows that this patch fixes bug 1538953.
> > > 
> > > CC: Alex Williamson <alex.williamson@redhat.com>
> > > CC: Marcel Apfelbaum <marcel@redhat.com>
> > > CC: Michael S. Tsirkin <mst@redhat.com>
> > > CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > > CC: Juan Quintela <quintela@redhat.com>
> > > CC: Laurent Vivier <lvivier@redhat.com>
> > > Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1538953
> > > Reported-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> > > Signed-off-by: Peter Xu <peterx@redhat.com>
> > > ---
> > > Marcel & all,
> > > 
> > > I think it's possible that we need similar thing for other bridge-like
> > > devices, but I'm not that familiar.  Would you help confirm?  Thanks,
> > 
> > Is a pity we don't have a way to mark the migration priority
> > in a base class. Dave, maybe we do have a way?
> > 
> > In the meantime you would need to add it also to:
> > - ioh3420 (Intel root port)
> > - xio3130_downstream (Intel switch downstream port)
> > - xio3130_upstream (The counterpart of the above, you want the whole
> >   switch to be migrated before loading the IOMMU device state)
> > - pcie_pci_bridge (for pci devices)
> > - pci-pci bridge (if for some reason you have one attached to the pcie_pci_brdge)
> > - i82801b11 (dmi-pci bridge, we want to deprecate it bu is there for now)
> > 
> > Thanks,
> > Marcel
> 
> It's kind of strange that we need to set the priority manually.
> Can't migration figure it out itself?

> I think bus
> must always be migrated before the devices behind it ...

I think that's true; but:
  a) Is the iommu a child of any of the PCI busses?
  b) does anything ensure that the bridge that's a parent of a bus
     gets migrated before the bus it provides?
  c) What happens with more htan one root port?

Dave


> > >  hw/pci-bridge/gen_pcie_root_port.c | 1 +
> > >  include/migration/vmstate.h        | 1 +
> > >  2 files changed, 2 insertions(+)
> > > 
> > > diff --git a/hw/pci-bridge/gen_pcie_root_port.c b/hw/pci-bridge/gen_pcie_root_port.c
> > > index 0e2f2e8bf1..e6ff1effd8 100644
> > > --- a/hw/pci-bridge/gen_pcie_root_port.c
> > > +++ b/hw/pci-bridge/gen_pcie_root_port.c
> > > @@ -101,6 +101,7 @@ static void gen_rp_realize(DeviceState *dev, Error **errp)
> > >  
> > >  static const VMStateDescription vmstate_rp_dev = {
> > >      .name = "pcie-root-port",
> > > +    .priority = MIG_PRI_PCIE_ROOT_PORT,
> > >      .version_id = 1,
> > >      .minimum_version_id = 1,
> > >      .post_load = pcie_cap_slot_post_load,
> > > diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> > > index 8c3889433c..491449db9f 100644
> > > --- a/include/migration/vmstate.h
> > > +++ b/include/migration/vmstate.h
> > > @@ -148,6 +148,7 @@ enum VMStateFlags {
> > >  typedef enum {
> > >      MIG_PRI_DEFAULT = 0,
> > >      MIG_PRI_IOMMU,              /* Must happen before PCI devices */
> > > +    MIG_PRI_PCIE_ROOT_PORT,     /* Must happen before IOMMU */
> > >      MIG_PRI_GICV3_ITS,          /* Must happen before PCI devices */
> > >      MIG_PRI_GICV3,              /* Must happen before the ITS */
> > >      MIG_PRI_MAX,
> > > 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK