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

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

* Peter Xu (peterx@redhat.com) 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.

Two questions (partially overlapping with what I replied to Michaels):
  a) What happens with multiple IOMMUs?
  b) What happens with multiple root ports?
  c) How correct is this ordering on different implementations 
    (e.g. ARM/Power/etc)

Dave

> 
> 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,
> ---
>  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,
> -- 
> 2.14.3
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK