RE: [PATCH v1 1/8] vfio: Add VFIO_IOMMU_PASID_REQUEST(alloc/free)

[Liu, Yi L]

> From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Sent: Tuesday, March 31, 2020 3:54 PM
> To: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> Subject: Re: [PATCH v1 1/8] vfio: Add VFIO_IOMMU_PASID_REQUEST(alloc/free)
> 
> Who is going to use thse exports?  Please submit them together with
> a driver actually using them.

Hi Hellwig,

These are exposed for SVA (Shared Virtual Addressing) usage in VMs. If
say a driver who actually using them, it is the iommu driver running in
guest. The flow is: guest iommu driver programs the virtual command interface
and it traps to host. The virtual IOMMU device model lays in QEMU will
utilize the exported ioctl to get PASIDs.
Here is iommu kernel driver patch which utilizes virtual command interface
to request pasid alloc/free.
https://lkml.org/lkml/2020/3/20/1176
And, the below patch is one which utilizes the ioctl exported in this patch:
https://patchwork.kernel.org/patch/11464601/

Regards,
Yi Liu