Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

Jason Gunthorpe
2021-03-30T13:07:55Z

On Fri, Mar 26, 2021 at 09:06:42AM +0100, Jean-Philippe Brucker wrote:

> It's not inconceivable to have a control queue doing DMA tagged with
> PASID. The devices I know either use untagged DMA, or have a choice to use
> a PASID.

I don't think we should encourage that. A PASID and all the related is
so expensive compared to just doing normal untagged kernel DMA.

I assume HW has these features because virtualization use cases might
use them, eg by using mdev to assign a command queue - then it would
need be be contained by a PASID.

Jason