Re: [PATCH v7 12/12] hw/acpi: Make the PCI hot-plug aware of SR-IOV

[Michael S. Tsirkin]

On Fri, Mar 18, 2022 at 08:18:19PM +0100, Lukasz Maniak wrote:
> 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>

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

feel free to include when merging the rest of the patchset.

> ---
>  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