Re: [PATCH 01/12] iommu: Add new iommu op to create domains owned by userspace

[Nicolin Chen <nicolinc@nvidia.com>]

Hi Jason,

On Thu, Mar 09, 2023 at 08:56:06PM -0400, Jason Gunthorpe wrote:
> On Thu, Mar 09, 2023 at 12:08:59AM -0800, Yi Liu wrote:
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index 3ef84ee359d2..a269bc62a31c 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -229,6 +229,7 @@ struct iommu_iotlb_gather {
> >   *           after use. Return the data buffer if success, or ERR_PTR on
> >   *           failure.
> >   * @domain_alloc: allocate iommu domain
> > + * @domain_alloc_user: allocate user iommu domain
> >   * @probe_device: Add device to iommu driver handling
> >   * @release_device: Remove device from iommu driver handling
> >   * @probe_finalize: Do final setup work after the device is added to an IOMMU
> > @@ -266,6 +267,9 @@ struct iommu_ops {
> >  
> >  	/* Domain allocation and freeing by the iommu driver */
> >  	struct iommu_domain *(*domain_alloc)(unsigned iommu_domain_type);
> > +	struct iommu_domain *(*domain_alloc_user)(struct device *dev,
> > +						  struct iommu_domain *parent,
> > +						  const void *user_data);
> 
> Since the kernel does the copy from user and manages the zero fill
> compat maybe this user_data have a union like Robin suggested.
> 
> But yes, this is the idea.
> 
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

We pass in a read-only data to this ->domain_alloc_user() while
it also returns NULL on failure, matching ->domain_alloc(). So,
there seems to be no error feedback pathway from the driver to
user space.

Robin remarked in the SMMU series that an STE configuration can
fail. So, a proper error feedback is required for this callback
too.

To return a driver/HW specific error, I think we could define a
"u8 out_error" in the user_data structure. So, we probably need
a non-const pass-in here. What do you think?

Thanks
Nic