Re: [PATCH v4 6/9] iommufd: Reserved -1 in the iommufd xarray

Jason Gunthorpe
2023-04-27T11:55:29Z

On Thu, Apr 27, 2023 at 07:09:38AM +0000, Liu, Yi L wrote:
> > > @@ -50,7 +53,7 @@ struct iommufd_object *_iommufd_object_alloc(struct
> > > iommufd_ctx *ictx,
> > > * before calling iommufd_object_finalize().
> > > */
> > > rc = xa_alloc(&ictx->objects, &obj->id, XA_ZERO_ENTRY,
> > > - xa_limit_32b, GFP_KERNEL_ACCOUNT);
> > > + iommufd_xa_limit_32b, GFP_KERNEL_ACCOUNT);
> >
> > Just direct use XA_LIMIT() here.
>
> Ok.
>
> > btw do we need a contract so vfio can learn 0 and -1 are reserved or
> > fine to have a fixed assumption in later patches?
>
> I doubt how to do it. ☹ @Jason? What about your opinion?

It is probably fine to use xa_limit_31b and just say that -ve values
are reserved in a comment near the define for 0

Jason