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

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, May 04, 2021 at 03:11:54PM -0700, Jacob Pan wrote:

> > It is a weird way to use xarray to have a structure which
> > itself is just a wrapper around another RCU protected structure.
> > 
> > Make the caller supply the ioasid_data memory, embedded in its own
> > element, get rid of the void * and rely on XA_ZERO_ENTRY to hold
> > allocated but not active entries.
> > 
> Let me try to paraphrase to make sure I understand. Currently
> struct ioasid_data is private to the iasid core, its memory is allocated by
> the ioasid core.
> 
> You are suggesting the following:
> 1. make struct ioasid_data public
> 2. caller allocates memory for ioasid_data, initialize it then pass it to
> ioasid_alloc to store in the xarray
> 3. caller will be responsible for setting private data inside ioasid_data
> and do call_rcu after update if needed.

Basically, but you probably won't need a "private data" once the
caller has this struct as it can just embed it in whatever larger
struct makes sense for it and use container_of/etc

I didn't look too closely at the whole thing though. Honestly I'm a
bit puzzled why we need a pluggable global allocator framework.. The
whole framework went to some trouble to isolate everything into iommu
drivers then that whole design is disturbed by this global thing.

Jason