On 9/18/25 10:57 AM, Zhenzhong Duan wrote:
> Call pci_device_get_viommu_flags() to get if vIOMMU supports
> VIOMMU_FLAG_WANT_NESTING_PARENT.
>
> If yes, create a nesting parent HWPT and add it to the container's hwpt_list,
> letting this parent HWPT cover the entire second stage mappings (GPA=>HPA).
>
> This allows a VFIO passthrough device to directly attach to this default HWPT
> and then to use the system address space and its listener.
>
> Introduce a vfio_device_get_viommu_flags_want_nesting() helper to facilitate
> this implementation.
>
> It is safe to do so because a vIOMMU will be able to fail in
> set_iommu_device()
> call, if something else related to the VFIO device or vIOMMU isn't compatible.
>
> Suggested-by: Nicolin Chen <[email protected]>
> Suggested-by: Yi Liu <[email protected]>
> Signed-off-by: Zhenzhong Duan <[email protected]>
> Reviewed-by: Nicolin Chen <[email protected]>
Reviewed-by: Eric Auger <[email protected]>
Eric
> ---
> include/hw/vfio/vfio-device.h | 2 ++
> hw/vfio/device.c | 12 ++++++++++++
> hw/vfio/iommufd.c | 9 +++++++++
> 3 files changed, 23 insertions(+)
>
> diff --git a/include/hw/vfio/vfio-device.h b/include/hw/vfio/vfio-device.h
> index e7e6243e2d..a964091135 100644
> --- a/include/hw/vfio/vfio-device.h
> +++ b/include/hw/vfio/vfio-device.h
> @@ -257,6 +257,8 @@ void vfio_device_prepare(VFIODevice *vbasedev,
> VFIOContainerBase *bcontainer,
>
> void vfio_device_unprepare(VFIODevice *vbasedev);
>
> +bool vfio_device_get_viommu_flags_want_nesting(VFIODevice *vbasedev);
> +
> int vfio_device_get_region_info(VFIODevice *vbasedev, int index,
> struct vfio_region_info **info);
> int vfio_device_get_region_info_type(VFIODevice *vbasedev, uint32_t type,
> diff --git a/hw/vfio/device.c b/hw/vfio/device.c
> index 08f12ac31f..620cc78b77 100644
> --- a/hw/vfio/device.c
> +++ b/hw/vfio/device.c
> @@ -23,6 +23,7 @@
>
> #include "hw/vfio/vfio-device.h"
> #include "hw/vfio/pci.h"
> +#include "hw/iommu.h"
> #include "hw/hw.h"
> #include "trace.h"
> #include "qapi/error.h"
> @@ -504,6 +505,17 @@ void vfio_device_unprepare(VFIODevice *vbasedev)
> vbasedev->bcontainer = NULL;
> }
>
> +bool vfio_device_get_viommu_flags_want_nesting(VFIODevice *vbasedev)
> +{
> + VFIOPCIDevice *vdev = vfio_pci_from_vfio_device(vbasedev);
> +
> + if (vdev) {
> + return !!(pci_device_get_viommu_flags(&vdev->parent_obj) &
> + VIOMMU_FLAG_WANT_NESTING_PARENT);
> + }
> + return false;
> +}
> +
> /*
> * Traditional ioctl() based io
> */
> diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
> index 8c27222f75..f1684a39b7 100644
> --- a/hw/vfio/iommufd.c
> +++ b/hw/vfio/iommufd.c
> @@ -379,6 +379,15 @@ static bool iommufd_cdev_autodomains_get(VFIODevice
> *vbasedev,
> flags = IOMMU_HWPT_ALLOC_DIRTY_TRACKING;
> }
>
> + /*
> + * If vIOMMU requests VFIO's cooperation to create nesting parent HWPT,
> + * force to create it so that it could be reused by vIOMMU to create
> + * nested HWPT.
> + */
> + if (vfio_device_get_viommu_flags_want_nesting(vbasedev)) {
> + flags |= IOMMU_HWPT_ALLOC_NEST_PARENT;
> + }
> +
> if (cpr_is_incoming()) {
> hwpt_id = vbasedev->cpr.hwpt_id;
> goto skip_alloc;
