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

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Date:   Thu, 13 Apr 2023 08:37:14 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     Yi Liu <yi.l.liu@...el.com>, joro@...tes.org,
        alex.williamson@...hat.com, kevin.tian@...el.com,
        robin.murphy@....com, baolu.lu@...ux.intel.com, cohuck@...hat.com,
        eric.auger@...hat.com, kvm@...r.kernel.org, mjrosato@...ux.ibm.com,
        chao.p.peng@...ux.intel.com, yi.y.sun@...ux.intel.com,
        peterx@...hat.com, jasowang@...hat.com,
        shameerali.kolothum.thodi@...wei.com, lulu@...hat.com,
        suravee.suthikulpanit@....com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 01/12] iommu: Add new iommu op to create domains owned by
 userspace

On Wed, Apr 12, 2023 at 05:44:04PM -0700, Nicolin Chen wrote:
> 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@...dia.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?

Jason