>-----Original Message-----
>From: Liu, Yi L <yi.l....@intel.com>
>Subject: Re: [PATCH v6 05/22] hw/pci: Introduce
>pci_device_get_viommu_flags()
>
>On 2025/9/18 16:57, 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.
>> 3. host IOMMU capabilities are passed to vIOMMU through
>set_iommu_device()
>> interface which have to be after attach_device(), when
>get_viommu_flags()
>> is called in attach_device(), there is no way for vIOMMU to get host
>> IOMMU capabilities yet, so only pure vIOMMU flags can be returned.
>> 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....@intel.com>
>> Signed-off-by: Zhenzhong Duan <zhenzhong.d...@intel.com>
>> ---
>> MAINTAINERS | 1 +
>> include/hw/iommu.h | 19 +++++++++++++++++++
>> include/hw/pci/pci.h | 27 +++++++++++++++++++++++++++
>> hw/pci/pci.c | 11 +++++++++++
>> 4 files changed, 58 insertions(+)
>> create mode 100644 include/hw/iommu.h
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index f8cd513d8b..71457e4cde 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -2307,6 +2307,7 @@ 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..65d652950a
>> --- /dev/null
>> +++ b/include/hw/iommu.h
>> @@ -0,0 +1,19 @@
>> +/*
>> + * 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"
>> +
>> +enum {
>> + /* Nesting parent HWPT will be reused by vIOMMU to create nested
>HWPT */
>
>vIOMMU needs nesting parent HWPT to create nested HWPT
Will do.
Thanks
Zhenzhong
