Re: [PATCH v3 04/20] vfio/iommufd: Force creating nested parent domain

[Eric Auger <eric.auger@redhat.com>]

On 7/8/25 1:05 PM, Zhenzhong Duan wrote:
> Call pci_device_get_viommu_cap() to get if vIOMMU supports VIOMMU_CAP_STAGE1,
> if yes, create nested parent domain which could be reused by vIOMMU to create
> nested domain.
>
> It is safe because hw_caps & VIOMMU_CAP_STAGE1 cannot be set yet because
> s->flts is forbidden until we support passthrough device with x-flts=on.
Reviewed-by: Eric Auger <eric.auger@redhat.com>

Eric

>
> Suggested-by: Nicolin Chen <nicolinc@nvidia.com>
> Suggested-by: Yi Liu <yi.l.liu@intel.com>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
> ---
>  hw/vfio/iommufd.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
> index 48c590b6a9..c172c177fc 100644
> --- a/hw/vfio/iommufd.c
> +++ b/hw/vfio/iommufd.c
> @@ -20,6 +20,7 @@
>  #include "trace.h"
>  #include "qapi/error.h"
>  #include "system/iommufd.h"
> +#include "hw/iommu.h"
>  #include "hw/qdev-core.h"
>  #include "hw/vfio/vfio-cpr.h"
>  #include "system/reset.h"
> @@ -379,6 +380,19 @@ static bool iommufd_cdev_autodomains_get(VFIODevice *vbasedev,
>          flags = IOMMU_HWPT_ALLOC_DIRTY_TRACKING;
>      }
>  
> +    /*
> +     * If vIOMMU supports stage-1 translation, force to create nested parent
> +     * domain which could be reused by vIOMMU to create nested domain.
> +     */
> +    if (vbasedev->type == VFIO_DEVICE_TYPE_PCI) {
> +        VFIOPCIDevice *vdev = container_of(vbasedev, VFIOPCIDevice, vbasedev);
> +
> +        hw_caps = pci_device_get_viommu_cap(&vdev->pdev);
> +        if (hw_caps & VIOMMU_CAP_STAGE1) {
> +            flags |= IOMMU_HWPT_ALLOC_NEST_PARENT;
> +        }
> +    }
> +
>      if (cpr_is_incoming()) {
>          hwpt_id = vbasedev->cpr.hwpt_id;
>          goto skip_alloc;