Re: [PATCH 0/4] Fix broken PCIe device after migration

[Michael S. Tsirkin]

On Thu, Feb 24, 2022 at 12:44:07PM -0500, Igor Mammedov wrote:
> Currently ACPI PCI hotplug is enabled by default for Q35 machine
> type and overrides native PCIe hotplug. It works as expected when
> a PCIe device is hotplugged into slot, however the device becomes
> in-operational after migration. Which is caused by BARs being
> disabled on target due to powered off status of the slot.
> 
> Proposed fix disables power control on PCIe slot when ACPI pcihp
> takes over hotplug control and makes PCIe slot check if power
> control is enabled before trying to change slot's power. Which
> leaves slot always powered on and that makes PCI core keep BARs
> enabled.
> 
> PS:
> it's still hacky approach as all ACPI PCI hotplug is, but it's
> the least intrusive one. Alternative, I've considered, could be
> chaining hotplug callbacks and making pcihp ones call overriden
> native callbacks while inhibiting hotplug event in native callbacks
> somehow. But that were a bit more intrusive and spills over to SHPC
> if implemented systematically, so I ditched that for now. It could
> be resurrected later on if current approach turns out to be
> insufficient.

Yes, I am wondering about this myself. Replace callbacks with
some kind of notifier, so instead of overrides we add things?
I will ponder this over the weekend.

> RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=2053584
> CC: mst@redhat.com
> CC: kraxel@redhat.com
> 
> Igor Mammedov (4):
>   pci: expose TYPE_XIO3130_DOWNSTREAM name
>   pcie: update slot power status only is power control is enabled
>   acpi: pcihp: disable power control on PCIe slot
>   q35: compat: keep hotplugged PCIe device broken after migration for
>     6.2-older machine types
> 
>  include/hw/acpi/pcihp.h                    |  4 +++-
>  include/hw/pci-bridge/xio3130_downstream.h | 15 +++++++++++++++
>  hw/acpi/acpi-pci-hotplug-stub.c            |  3 ++-
>  hw/acpi/ich9.c                             | 21 ++++++++++++++++++++-
>  hw/acpi/pcihp.c                            | 16 +++++++++++++++-
>  hw/acpi/piix4.c                            |  3 ++-
>  hw/core/machine.c                          |  4 +++-
>  hw/pci-bridge/xio3130_downstream.c         |  3 ++-
>  hw/pci/pcie.c                              |  5 ++---
>  9 files changed, 64 insertions(+), 10 deletions(-)
>  create mode 100644 include/hw/pci-bridge/xio3130_downstream.h
> 
> -- 
> 2.31.1