Re: [PATCH v4] pci-bridge: avoid linking a single downstream port more than once

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

On Thu, Jul 25, 2024 at 05:38:19AM -0400, Yao Xingtao wrote:
> Since the downstream port is not checked, two slots can be linked to
> a single port. However, this can prevent the driver from detecting the
> device properly.
> 
> It is necessary to ensure that a downstream port is not linked more than
> once.
> 
> Links: https://lore.kernel.org/qemu-devel/OSZPR01MB6453BC61D2FF4035F18084EF8DDC2@OSZPR01MB6453.jpnprd01.prod.outlook.com
> Signed-off-by: Yao Xingtao <yaoxt.fnst@fujitsu.com>
> 
> ---
> V3[3] -> V4:
>  - make the error message more readable
>  - fix the downstream port check error
> 
> V2[2] -> V3:
>  - Move this check into pcie_cap_init()
> 
> V1[1] -> V2:
>  - Move downstream port check forward
> 
> [1] https://lore.kernel.org/qemu-devel/20240704033834.3362-1-yaoxt.fnst@fujitsu.com
> [2] https://lore.kernel.org/qemu-devel/20240717085621.55315-1-yaoxt.fnst@fujitsu.com
> [3] https://lore.kernel.org/qemu-devel/20240725032731.13032-1-yaoxt.fnst@fujitsu.com
> ---
>  hw/pci/pcie.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> index 4b2f0805c6e0..1e53be1bc7c5 100644
> --- a/hw/pci/pcie.c
> +++ b/hw/pci/pcie.c
> @@ -192,6 +192,13 @@ int pcie_cap_init(PCIDevice *dev, uint8_t offset,
>  
>      assert(pci_is_express(dev));
>  
> +    if ((type == PCI_EXP_TYPE_DOWNSTREAM || type == PCI_EXP_TYPE_ROOT_PORT) &&
> +        pcie_find_port_by_pn(pci_get_bus(dev), port)) {
> +        error_setg(errp, "The port %d is already in use, please select "
> +                   "another port", port);
> +        return -EBUSY;
> +    }
> +
>      pos = pci_add_capability(dev, PCI_CAP_ID_EXP, offset,
>                               PCI_EXP_VER2_SIZEOF, errp);
>      if (pos < 0) {


But can't there be two functions of a multi-function device,
sharing a port?

> -- 
> 2.41.0