Re: [PATCH v7 10/12] vpci: add initial support for virtual PCI bus topology

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.06.2023 12:32, Volodymyr Babchuk wrote:
> @@ -121,6 +124,62 @@ int vpci_add_handlers(struct pci_dev *pdev)
>  }
>  
>  #ifdef CONFIG_HAS_VPCI_GUEST_SUPPORT
> +static int add_virtual_device(struct pci_dev *pdev)
> +{
> +    struct domain *d = pdev->domain;
> +    pci_sbdf_t sbdf = { 0 };
> +    unsigned long new_dev_number;
> +
> +    if ( is_hardware_domain(d) )
> +        return 0;
> +
> +    ASSERT(pcidevs_locked());
> +
> +    /*
> +     * Each PCI bus supports 32 devices/slots at max or up to 256 when
> +     * there are multi-function ones which are not yet supported.
> +     */
> +    if ( pdev->info.is_extfn )
> +    {
> +        gdprintk(XENLOG_ERR, "%pp: only function 0 passthrough supported\n",
> +                 &pdev->sbdf);
> +        return -EOPNOTSUPP;
> +    }
> +
> +    new_dev_number = find_first_zero_bit(d->vpci_dev_assigned_map,
> +                                         VPCI_MAX_VIRT_DEV);
> +    if ( new_dev_number >= VPCI_MAX_VIRT_DEV )
> +        return -ENOSPC;
> +
> +    __set_bit(new_dev_number, &d->vpci_dev_assigned_map);

Since the find-and-set can't easily be atomic, the lock used here (
asserted to be held above) needs to be the same as ...

> +    /*
> +     * Both segment and bus number are 0:
> +     *  - we emulate a single host bridge for the guest, e.g. segment 0
> +     *  - with bus 0 the virtual devices are seen as embedded
> +     *    endpoints behind the root complex
> +     *
> +     * TODO: add support for multi-function devices.
> +     */
> +    sbdf.devfn = PCI_DEVFN(new_dev_number, 0);
> +    pdev->vpci->guest_sbdf = sbdf;
> +
> +    return 0;
> +
> +}
> +
> +static void vpci_remove_virtual_device(const struct pci_dev *pdev)
> +{
> +    write_lock(&pdev->domain->vpci_rwlock);
> +    if ( pdev->vpci )
> +    {
> +        __clear_bit(pdev->vpci->guest_sbdf.dev,
> +                    &pdev->domain->vpci_dev_assigned_map);
> +        pdev->vpci->guest_sbdf.sbdf = ~0;
> +    }
> +    write_unlock(&pdev->domain->vpci_rwlock);

... the one used here.

Jan