Re: [PATCH v7 05/23] hw/pci: Introduce pci_device_get_viommu_flags()

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

On 10/28/25 7:57 AM, Duan, Zhenzhong wrote:
>
>> -----Original Message-----
>> From: Cédric Le Goater <clg@redhat.com>
>> Subject: Re: [PATCH v7 05/23] hw/pci: Introduce
>> pci_device_get_viommu_flags()
>>
>> On 10/24/25 10:43, Zhenzhong Duan wrote:
>>> Introduce a new PCIIOMMUOps optional callback, get_viommu_flags()
>> which
>>> allows to retrieve flags exposed by a vIOMMU. The first planned vIOMMU
>>> device flag is VIOMMU_FLAG_WANT_NESTING_PARENT that advertises the
>>> support of HW nested stage translation scheme and wants other sub-system
>>> like VFIO's cooperation to create nesting parent HWPT.
>>>
>>> pci_device_get_viommu_flags() is a wrapper that can be called on a PCI
>>> device potentially protected by a vIOMMU.
>>>
>>> get_viommu_flags() is designed to return 64bit bitmap of purely vIOMMU
>>> flags 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.
>>>
>>> Note that this op will be invoked at the attach_device() stage, at which
>>> point host IOMMU capabilities are not yet forwarded to the vIOMMU
>> through
>>> the set_iommu_device() callback that will be after the attach_device().
>>>
>>> See below sequence:
>>>
>>>    vfio_device_attach():
>>>        iommufd_cdev_attach():
>>>            pci_device_get_viommu_flags() 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.liu@intel.com>
>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>>> Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
>>> Reviewed-by: Eric Auger <eric.auger@redhat.com>
>>> Reviewed-by: Yi Liu <yi.l.liu@intel.com>
>>> ---
>>>   MAINTAINERS          |  1 +
>>>   include/hw/iommu.h   | 25 +++++++++++++++++++++++++
>>
>> Hmm, why not under include/hw/pci/ ?
> I'm not sure if it's better to restrict iommu to pci subsystem.
> I have a vague memory there is iommu supporting non-PCI devices.

effectively on ARM we may need to support SMMU for platform devices too

Eric
>
>> Was this discussed ?
> No.
>
> Thanks
> Zhenzhong
>
>>
>> Reviewed-by: Cédric Le Goater <clg@redhat.com>
>>
>> Thanks,
>>
>> C.
>>
>>
>>
>>>   include/hw/pci/pci.h | 22 ++++++++++++++++++++++
>>>   hw/pci/pci.c         | 11 +++++++++++
>>>   4 files changed, 59 insertions(+)
>>>   create mode 100644 include/hw/iommu.h
>>>
>>> diff --git a/MAINTAINERS b/MAINTAINERS
>>> index 36eef27b41..d94fbcbdfb 100644
>>> --- a/MAINTAINERS
>>> +++ b/MAINTAINERS
>>> @@ -2338,6 +2338,7 @@ F: include/system/iommufd.h
>>>   F: backends/host_iommu_device.c
>>>   F: include/system/host_iommu_device.h
>>>   F: include/qemu/chardev_open.h
>>> +F: include/hw/iommu.h
>>>   F: util/chardev_open.c
>>>   F: docs/devel/vfio-iommufd.rst
>>>
>>> diff --git a/include/hw/iommu.h b/include/hw/iommu.h
>>> new file mode 100644
>>> index 0000000000..9b8bb94fc2
>>> --- /dev/null
>>> +++ b/include/hw/iommu.h
>>> @@ -0,0 +1,25 @@
>>> +/*
>>> + * General vIOMMU flags
>>> + *
>>> + * Copyright (C) 2025 Intel Corporation.
>>> + *
>>> + * SPDX-License-Identifier: GPL-2.0-or-later
>>> + */
>>> +
>>> +#ifndef HW_IOMMU_H
>>> +#define HW_IOMMU_H
>>> +
>>> +#include "qemu/bitops.h"
>>> +
>>> +/*
>>> + * Theoretical vIOMMU flags. Only determined by the vIOMMU device
>> properties and
>>> + * independent on the actual host IOMMU capabilities they may depend on.
>> Each
>>> + * flag can be an expectation or request to other sub-system or just a pure
>>> + * vIOMMU capability. vIOMMU can choose which flags to expose.
>>> + */
>>> +enum viommu_flags {
>>> +    /* vIOMMU needs nesting parent HWPT to create nested HWPT */
>>> +    VIOMMU_FLAG_WANT_NESTING_PARENT = BIT_ULL(0),
>>> +};
>>> +
>>> +#endif /* HW_IOMMU_H */
>>> diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
>>> index bde9dca8e2..cf99b5bb68 100644
>>> --- a/include/hw/pci/pci.h
>>> +++ b/include/hw/pci/pci.h
>>> @@ -462,6 +462,18 @@ typedef struct PCIIOMMUOps {
>>>        * @devfn: device and function number of the PCI device.
>>>        */
>>>       void (*unset_iommu_device)(PCIBus *bus, void *opaque, int devfn);
>>> +    /**
>>> +     * @get_viommu_flags: get vIOMMU flags
>>> +     *
>>> +     * Optional callback, if not implemented, then vIOMMU doesn't
>> support
>>> +     * exposing flags to other sub-system, e.g., VFIO.
>>> +     *
>>> +     * @opaque: the data passed to pci_setup_iommu().
>>> +     *
>>> +     * Returns: bitmap with each representing a vIOMMU flag defined in
>>> +     * enum viommu_flags.
>>> +     */
>>> +    uint64_t (*get_viommu_flags)(void *opaque);
>>>       /**
>>>        * @get_iotlb_info: get properties required to initialize a device
>> IOTLB.
>>>        *
>>> @@ -644,6 +656,16 @@ bool pci_device_set_iommu_device(PCIDevice
>> *dev, HostIOMMUDevice *hiod,
>>>                                    Error **errp);
>>>   void pci_device_unset_iommu_device(PCIDevice *dev);
>>>
>>> +/**
>>> + * pci_device_get_viommu_flags: get vIOMMU flags.
>>> + *
>>> + * Returns: bitmap with each representing a vIOMMU flag defined in
>>> + * enum viommu_flags. Or 0 if vIOMMU doesn't report any.
>>> + *
>>> + * @dev: PCI device pointer.
>>> + */
>>> +uint64_t pci_device_get_viommu_flags(PCIDevice *dev);
>>> +
>>>   /**
>>>    * pci_iommu_get_iotlb_info: get properties required to initialize a
>>>    * device IOTLB.
>>> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
>>> index d0e81651aa..c9932c87e3 100644
>>> --- a/hw/pci/pci.c
>>> +++ b/hw/pci/pci.c
>>> @@ -3010,6 +3010,17 @@ void
>> pci_device_unset_iommu_device(PCIDevice *dev)
>>>       }
>>>   }
>>>
>>> +uint64_t pci_device_get_viommu_flags(PCIDevice *dev)
>>> +{
>>> +    PCIBus *iommu_bus;
>>> +
>>> +    pci_device_get_iommu_bus_devfn(dev, &iommu_bus, NULL, NULL);
>>> +    if (iommu_bus && iommu_bus->iommu_ops->get_viommu_flags) {
>>> +        return
>> iommu_bus->iommu_ops->get_viommu_flags(iommu_bus->iommu_opaque);
>>> +    }
>>> +    return 0;
>>> +}
>>> +
>>>   int pci_pri_request_page(PCIDevice *dev, uint32_t pasid, bool priv_req,
>>>                            bool exec_req, hwaddr addr, bool lpig,
>>>                            uint16_t prgi, bool is_read, bool is_write)