RE: [PATCH v1 02/14] iommufd: Add nesting related data structures for ARM SMMUv3

Tian, Kevin
2023-03-17T10:18:10Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Friday, March 10, 2023 8:52 PM
>
> On Fri, Mar 10, 2023 at 12:33:12PM +0100, Eric Auger wrote:
>
> > I do agree with Jean. We spent a lot of efforts all together to define
> > this generic invalidation API and if there is compelling reason that
> > prevents from using it, we should try to reuse it.
>
> That's the compelling reason in a nutshell right there.
>
> Alot of time was invested to create something that might be
> general. We still don't know if it is well defined and general. Even
> more time is going to be required on it before it could go forward. In
> future more time will be needed for every future HW to try and fit
> into it. We don't even know if it will scale to future HW. Nobody has
> even checked what today's POWER and S390 HW need.
>
> vs, this stuff was made in a few days. We know it is correct as a uAPI
> since it mirrors the HW and we know it is scalable to different HW
> schemes if they come up.
>
> So I don't see a good reason to take a risk on a "general" uAPI. If we
> make this wrong it could seriously damage the main goal of iommufd -
> to build accelerated vIOMMU models.
>

I'm with this point. We can add a virtio format when it comes.