Re: [PATCH 1/4] ioasid: Reserve a global PASID for in-kernel DMA

[Jason Gunthorpe]

On Fri, Dec 10, 2021 at 09:06:24AM +0000, Jean-Philippe Brucker wrote:
> On Thu, Dec 09, 2021 at 10:14:04AM -0800, Jacob Pan wrote:
> > > This looks like we're just one step away from device drivers needing
> > > multiple PASIDs for kernel DMA so I'm trying to figure out how to evolve
> > > the API towards that. It's probably as simple as keeping a kernel IOASID
> > > set at first, but then we'll probably want to optimize by having multiple
> > > overlapping sets for each device driver (all separate from the SVA set).
> > Sounds reasonable to start with a kernel set for in-kernel DMA once we need
> > multiple ones. But I am not sure what *overlapping* sets mean here, could
> > you explain?
> 
> Given that each device uses a separate PASID table, we could allocate the
> same set of PASID values for different device drivers. We just need to
> make sure that those values are different from PASIDs allocated for user
> SVA.

Why does user SVA need global values anyhow?

Jason