[PATCH v6 12/12] hw/acpi: Make the PCI hot-plug aware of SR-IOV

[Lukasz Maniak <lukasz.maniak@linux.intel.com>]

From: Łukasz Gieryk <lukasz.gieryk@linux.intel.com>

PCI device capable of SR-IOV support is a new, still-experimental
feature with only a single working example of the Nvme device.

This patch in an attempt to fix a double-free problem when a
SR-IOV-capable Nvme device is hot-unplugged. The problem and the
reproduction steps can be found in this thread:

https://patchew.org/QEMU/20220217174504.1051716-1-lukasz.maniak@linux.intel.com/20220217174504.1051716-14-lukasz.maniak@linux.intel.com/

Details of the proposed solution are, for convenience, included below.

1) The current SR-IOV implementation assumes it’s the PhysicalFunction
   that creates and deletes VirtualFunctions.
2) It’s a design decision (the Nvme device at least) for the VFs to be
   of the same class as PF. Effectively, they share the dc->hotpluggable
   value.
3) When a VF is created, it’s added as a child node to PF’s PCI bus
   slot.
4) Monitor/device_del triggers the ACPI mechanism. The implementation is
   not aware of SR/IOV and ejects PF’s PCI slot, directly unrealizing all
   hot-pluggable (!acpi_pcihp_pc_no_hotplug) children nodes.
5) VFs are unrealized directly, and it doesn’t work well with (1).
   SR/IOV structures are not updated, so when it’s PF’s turn to be
   unrealized, it works on stale pointers to already-deleted VFs.

Signed-off-by: Łukasz Gieryk <lukasz.gieryk@linux.intel.com>
---
 hw/acpi/pcihp.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
index 6351bd3424d..248839e1110 100644
--- a/hw/acpi/pcihp.c
+++ b/hw/acpi/pcihp.c
@@ -192,8 +192,12 @@ static bool acpi_pcihp_pc_no_hotplug(AcpiPciHpState *s, PCIDevice *dev)
      * ACPI doesn't allow hotplug of bridge devices.  Don't allow
      * hot-unplug of bridge devices unless they were added by hotplug
      * (and so, not described by acpi).
+     *
+     * Don't allow hot-unplug of SR-IOV Virtual Functions, as they
+     * will be removed implicitly, when Physical Function is unplugged.
      */
-    return (pc->is_bridge && !dev->qdev.hotplugged) || !dc->hotpluggable;
+    return (pc->is_bridge && !dev->qdev.hotplugged) || !dc->hotpluggable ||
+           pci_is_vf(dev);
 }
 
 static void acpi_pcihp_eject_slot(AcpiPciHpState *s, unsigned bsel, unsigned slots)
-- 
2.25.1