RE: [PATCH v3 4/4] vfio/type1: Use iommu_aux_at(de)tach_group() APIs

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Wednesday, July 15, 2020 9:00 AM
> 
> Hi Christoph and Jacob,
> 
> On 7/15/20 12:29 AM, Jacob Pan wrote:
> > On Tue, 14 Jul 2020 09:25:14 +0100
> > Christoph Hellwig<hch@xxxxxxxxxxxxx>  wrote:
> >
> >> On Tue, Jul 14, 2020 at 01:57:03PM +0800, Lu Baolu wrote:
> >>> Replace iommu_aux_at(de)tach_device() with
> >>> iommu_aux_at(de)tach_group(). It also saves the
> >>> IOMMU_DEV_FEAT_AUX-capable physcail device in the vfio_group data
> >>> structure so that it could be reused in other places.
> >> This removes the last user of iommu_aux_attach_device and
> >> iommu_aux_detach_device, which can be removed now.
> > it is still used in patch 2/4 inside iommu_aux_attach_group(), right?
> >
> 
> There is a need to use this interface. For example, an aux-domain is
> attached to a subset of a physical device and used in the kernel. In
> this usage scenario, there's no need to use vfio/mdev. The device driver
> could just allocate an aux-domain and call iommu_aux_attach_device() to
> setup the iommu.
> 

and here is one example usage for adding per-instance pagetables for drm/msm:
https://lore.kernel.org/lkml/20200626200414.14382-5-jcrouse@xxxxxxxxxxxxxx/

Thanks
Kevin