RE: [PATCH v4 28/41] vfio/iommufd: Implement the iommufd backend

[Duan, Zhenzhong]

>-----Original Message-----
>From: Jason Gunthorpe <jgg@nvidia.com>
>Sent: Wednesday, November 8, 2023 10:19 PM
>Subject: Re: [PATCH v4 28/41] vfio/iommufd: Implement the iommufd backend
>
>On Wed, Nov 08, 2023 at 01:25:34PM +0000, Duan, Zhenzhong wrote:
>
>> >I was expecting that hwpt manipulation would be done exclusively
>> >inside the device-specific vIOMMU userspace driver. Generic code paths
>> >that don't have that knowledge should use the IOAS for everything
>>
>> Yes, this way we don't need to distinguish between mdev and real device,
>> just attach to IOAS. But lose the benefit that same hwpt could be passed
>> into vIOMMU to be used as S2 hwpt in nesting.
>
>If you have a nesting capable vIOMMU driver then it should be
>creating the HWPTs and managing them in its layer. Maybe the core code
>provides some helpers.

OK, thanks for suggestion.

>
>Obviously you can't link a mdev to a nesting vIOMMU driver in the
>first place. Mdev should be connected to a different IOMMU driver that
>doesn't use HWPT at all.
>
>I think it will make alot of trouble to put the hwpt in the wrong
>layer as there shouldn't really be much generic code touching it.

I'll send v5 with your suggested changes.

Thanks
Zhenzhong