Re: [PATCH v3] hw/pci: prevent hotplug of devices on pcie-root-ports on the wrong slot

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jun 19, 2023 at 09:29:26PM +0530, Ani Sinha wrote:
> When a device is plugged into a PCIE root port, it can only be plugged into slot
> 0. Hotplugging a device into a slot other than slot 0 is invalid and should be
> prevented. This change ensures that we throw an error if the user tries to plug
> a device into a pcie root port on any slot other than slot 0.
> 
> CC: jusual@redhat.com
> CC: imammedo@redhat.com
> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2128929
> Signed-off-by: Ani Sinha <anisinha@redhat.com>
> ---
>  hw/pci/pci.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> changelog:
> v2: addressed issue with multifunction pcie root ports. Should allow
> hotplug on functions other than function 0.
> v3: improved commit message.

Weird. You say you improved it but it still only mentions
root port while code works for downstream ports too.
Improve it some more please I guess ;)


> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index bf38905b7d..66999352cc 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -64,6 +64,7 @@ bool pci_available = true;
>  static char *pcibus_get_dev_path(DeviceState *dev);
>  static char *pcibus_get_fw_dev_path(DeviceState *dev);
>  static void pcibus_reset(BusState *qbus);
> +static bool pcie_has_upstream_port(PCIDevice *dev);
>  
>  static Property pci_props[] = {
>      DEFINE_PROP_PCI_DEVFN("addr", PCIDevice, devfn, -1),
> @@ -1182,6 +1183,11 @@ static PCIDevice *do_pci_register_device(PCIDevice *pci_dev,
>      } else if (dev->hotplugged &&
>                 !pci_is_vf(pci_dev) &&
>                 pci_get_function_0(pci_dev)) {
> +        /*
> +         * populating function 0 triggers a bus scan from the guest that
> +         * exposes other non-zero functions. Hence we need to ensure that
> +         * function 0 is available.

available -> wasn't added yet

> +         */
>          error_setg(errp, "PCI: slot %d function 0 already occupied by %s,"
>                     " new func %s cannot be exposed to guest.",
>                     PCI_SLOT(pci_get_function_0(pci_dev)->devfn),
> @@ -1189,6 +1195,16 @@ static PCIDevice *do_pci_register_device(PCIDevice *pci_dev,
>                     name);
>  
>         return NULL;
> +    } else if (dev->hotplugged &&
> +               !pci_is_vf(pci_dev) &&
> +               pcie_has_upstream_port(pci_dev) && PCI_SLOT(devfn)) {
> +        /*
> +         * If the device is being plugged into an upstream PCIE port,

No, it's not plugged into an upstream port. It *has* an upstream port.


> +         * like a pcie root port, we only support one device at slot 0

this is wrong too, in that "device" here is a pci function, we
support only slot 0, but many functions.

> +         */
> +        error_setg(errp, "PCI: slot %d is not valid for %s",


Let's not just complain, explain why ;)

> +                   PCI_SLOT(devfn), name);
> +        return NULL;
>      }
>  
>      pci_dev->devfn = devfn;
> -- 
> 2.39.1