>-----Original Message-----
>From: Nicolin Chen <nicol...@nvidia.com>
>Subject: Re: [PATCH v6 05/22] hw/pci: Introduce
>pci_device_get_viommu_flags()
>
>On Wed, Sep 24, 2025 at 07:05:42AM +0000, Duan, Zhenzhong wrote:
>> >From: Nicolin Chen <nicol...@nvidia.com>
>> >Subject: Re: [PATCH v6 05/22] hw/pci: Introduce
>> >> 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.
>> >
>> >"no way" sounds too strong..
>> >
>> >There is an iommufd_backend_get_device_info() call there. So, we
>> >could have passed the host IOMMU capabilities to a vIOMMU. Just,
>> >we chose not to (assuming for migration reason?).
>>
>> What about 'it's hard for vIOMMU to get host IOMMU...'?
>
>vfio-iommufd core code gets all the host IOMMU caps via the vfio
>device but chooses to not forward to vIOMMU. So, it's neither "no
>way" nor "hard" :)
Yes, that needs to introduce another callback to forward the caps early,
unnecessarily complex.
>
>To be honest, I don't feel this very related to be the reason 3
>to justify for the new op/API. 1 and 2 are quite okay?
>
>Having said that, it's probably good to add as a side note:
>
>"
>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 the below sequence:
>"
OK, will drop 3 and add the side note.
Thanks
Zhenzhong
