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

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, Apr 13, 2023 at 08:37:14AM -0300, Jason Gunthorpe wrote:

> > > > @@ -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?
> 
> What is wrong with err_ptr?

I see. That could keep the "const" then. Will try that.

Thanks!
Nic