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

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Message-ID: <ZDge7fiLQqKqwAUV@Asurada-Nvidia>
Date:   Thu, 13 Apr 2023 08:25:33 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Jason Gunthorpe <jgg@...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 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@...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?

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

Thanks!
Nic