Re: [PATCH v1 3/3] xen/pci: add discovered PCI device at boot

[Jan Beulich <jbeulich@xxxxxxxx>]

On 01.08.2025 11:22, Mykyta Poturai wrote:
> Create add_discovered_pci_devices function that calls pci_device_add
> on every PCI device discovered.
> The devices will be added to dom_io so that they can be assigned
> later to other domains.

And why's the intermediate step necessary? IOW can't they be assigned to their
target domains right away, and only whatever's left would go to DOM_IO?

> --- a/xen/drivers/passthrough/pci.c
> +++ b/xen/drivers/passthrough/pci.c
> @@ -1180,6 +1180,34 @@ int __init scan_pci_devices(void)
>      return ret;
>  }
>  
> +static int __init _add_discovered_pci_devices(struct pci_seg *pseg, void 
> *arg)
> +{
> +    struct pci_dev *pdev;
> +    int ret = 0;
> +
> +    list_for_each_entry ( pdev, &pseg->alldevs_list, alldevs_list )
> +    {
> +        ret = pci_add_device(dom_io, pdev->seg, pdev->bus, pdev->devfn, NULL,
> +                             NUMA_NO_NODE);
> +        if ( ret < 0 )
> +        {
> +            printk(XENLOG_ERR
> +                   "%pp: Failure adding the discovered pci device (Error 
> %d)\n",
> +                   &pdev->sbdf, ret);
> +            break;
> +        }
> +    }
> +
> +    return ret;
> +}
> +
> +void __init add_discovered_pci_devices(void)
> +{
> +    pcidevs_lock();
> +    pci_segments_iterate(_add_discovered_pci_devices, NULL);
> +    pcidevs_unlock();
> +}

This looks to merely be a specialized form of what ...

>  struct setup_hwdom {
>      struct domain *d;
>      int (*handler)(uint8_t devfn, struct pci_dev *pdev);

... follows below here. By generalizing what we have (perhaps from the top, i.e.
iommu_hwdom_init()), you'd also avoid violating Misra rule 2.1 on x86, as you 
add
unreachable code there.

Jan