On Fri, Aug 22, 2025 at 02:40:40AM -0400, Zhenzhong Duan wrote:
> Introduce a new PCIIOMMUOps optional callback, get_viommu_cap() which
> allows to retrieve capabilities exposed by a vIOMMU. The first planned
> vIOMMU device capability is VIOMMU_CAP_HW_NESTED that advertises the
> support of HW nested stage translation scheme. pci_device_get_viommu_cap
> is a wrapper that can be called on a PCI device potentially protected by
> a vIOMMU.
>
> get_viommu_cap() is designed to return 64bit bitmap of purely emulated
> capabilities which are only determined by user's configuration, no host
> capabilities involved. Reasons are:
>
> 1. host may has heterogeneous IOMMUs, each with different capabilities
> 2. this is migration friendly, return value is consistent between source
> and target.
> 3. host IOMMU capabilities are passed to vIOMMU through set_iommu_device()
> interface which have to be after attach_device(), when get_viommu_cap()
> is called in attach_device(), there is no way for vIOMMU to get host
> IOMMU capabilities yet, so only emulated capabilities can be returned.
> See below sequence:
>
> vfio_device_attach():
> iommufd_cdev_attach():
> pci_device_get_viommu_cap() for HW nesting cap
> create a nesting parent hwpt
> attach device to the hwpt
> vfio_device_hiod_create_and_realize() creating hiod
> ...
> pci_device_set_iommu_device(hiod)
>
> Suggested-by: Yi Liu <yi.l....@intel.com>
> Signed-off-by: Zhenzhong Duan <zhenzhong.d...@intel.com>
Reviewed-by: Nicolin Chen <nicol...@nvidia.com>
