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

[Marcel Apfelbaum]

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 <address@hidden>
> CC: Marcel Apfelbaum <address@hidden>
> CC: Michael S. Tsirkin <address@hidden>
> CC: Dr. David Alan Gilbert <address@hidden>
> CC: Juan Quintela <address@hidden>
> CC: Laurent Vivier <address@hidden>
> Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1538953
> Reported-by: Maxime Coquelin <address@hidden>
> Signed-off-by: Peter Xu <address@hidden>
> ---
> 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

>  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,
>