Re: [PATCH v5 08/32] hw/pci/pci: Add optional supports_address_space() callback

[Jonathan Cameron via <qemu-devel@nongnu.org>]

On Fri, 31 Oct 2025 10:49:41 +0000
Shameer Kolothum <skolothumtho@nvidia.com> wrote:

> Introduce an optional supports_address_space() callback in PCIIOMMUOps to
> allow a vIOMMU implementation to reject devices that should not be attached
> to it.
> 
> Currently, get_address_space() is the first and mandatory callback into the
> vIOMMU layer, which always returns an address space. For certain setups, such
> as hardware accelerated vIOMMUs (e.g. ARM SMMUv3 with accel=on), attaching
> emulated endpoint devices is undesirable as it may impact the behavior or
> performance of VFIO passthrough devices, for example, by triggering
> unnecessary invalidations on the host IOMMU.
> 
> The new callback allows a vIOMMU to check and reject unsupported devices
> early during PCI device registration.
LGTM
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>

> 
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
> ---
>  hw/pci/pci.c         | 20 ++++++++++++++++++++
>  include/hw/pci/pci.h | 17 +++++++++++++++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index 9693d7f10c..fa9cf5dab2 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -135,6 +135,21 @@ static void pci_set_master(PCIDevice *d, bool enable)
>      d->is_master = enable; /* cache the status */
>  }
>  
> +static bool
> +pci_device_supports_iommu_address_space(PCIDevice *dev, Error **errp)
> +{
> +    PCIBus *bus;
> +    PCIBus *iommu_bus;
> +    int devfn;
> +
> +    pci_device_get_iommu_bus_devfn(dev, &iommu_bus, &bus, &devfn);
> +    if (iommu_bus && iommu_bus->iommu_ops->supports_address_space) {
> +        return iommu_bus->iommu_ops->supports_address_space(bus,
> +                                iommu_bus->iommu_opaque, devfn, errp);
> +    }
> +    return true;
> +}
> +
>  static void pci_init_bus_master(PCIDevice *pci_dev)
>  {
>      AddressSpace *dma_as = pci_device_iommu_address_space(pci_dev);
> @@ -1413,6 +1428,11 @@ static PCIDevice *do_pci_register_device(PCIDevice *pci_dev,
>      pci_dev->config_write = config_write;
>      bus->devices[devfn] = pci_dev;
>      pci_dev->version_id = 2; /* Current pci device vmstate version */
> +    if (!pci_device_supports_iommu_address_space(pci_dev, errp)) {
> +        do_pci_unregister_device(pci_dev);
> +        bus->devices[devfn] = NULL;
> +        return NULL;
> +    }
>      if (phase_check(PHASE_MACHINE_READY)) {
>          pci_init_bus_master(pci_dev);
>      }
> diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
> index cf99b5bb68..dfeba8c9bd 100644
> --- a/include/hw/pci/pci.h
> +++ b/include/hw/pci/pci.h
> @@ -417,6 +417,23 @@ typedef struct IOMMUPRINotifier {
>   * framework for a set of devices on a PCI bus.
>   */
>  typedef struct PCIIOMMUOps {
> +    /**
> +     * @supports_address_space: Optional pre-check to determine if a PCI
> +     * device can have an IOMMU address space.
> +     *
> +     * @bus: the #PCIBus being accessed.
> +     *
> +     * @opaque: the data passed to pci_setup_iommu().
> +     *
> +     * @devfn: device and function number.
> +     *
> +     * @errp: pass an Error out only when return false
> +     *
> +     * Returns: true if the device can be associated with an IOMMU address
> +     * space, false otherwise with errp set.
> +     */
> +    bool (*supports_address_space)(PCIBus *bus, void *opaque, int devfn,
> +                                   Error **errp);
>      /**
>       * @get_address_space: get the address space for a set of devices
>       * on a PCI bus.