linux-kernel - Re: [PATCH v6 07/10] iommufd: Add a nested HW pagetable object

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Date:   Tue, 24 Oct 2023 10:50:58 -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>,
        <zhenzhong.duan@...el.com>, <joao.m.martins@...cle.com>
Subject: Re: [PATCH v6 07/10] iommufd: Add a nested HW pagetable object

On Tue, Oct 24, 2023 at 02:31:39PM -0300, Jason Gunthorpe wrote:
> On Tue, Oct 24, 2023 at 10:28:45AM -0700, Nicolin Chen wrote:
> > On Tue, Oct 24, 2023 at 02:18:10PM -0300, Jason Gunthorpe wrote:
> > > On Tue, Oct 24, 2023 at 08:06:06AM -0700, Yi Liu wrote:
> > > > @@ -195,6 +279,10 @@ int iommufd_hwpt_alloc(struct iommufd_ucmd *ucmd)
> > > >  	if (pt_obj->type == IOMMUFD_OBJ_IOAS) {
> > > >  		struct iommufd_hwpt_paging *hwpt_paging;
> > > >  
> > > > +		if (cmd->data_type != IOMMU_HWPT_DATA_NONE) {
> > > > +			rc = -EINVAL;
> > > > +			goto out_put_pt;
> > > > +		}
> > > >  		ioas = container_of(pt_obj, struct iommufd_ioas, obj);
> > > >  		mutex_lock(&ioas->mutex);
> > > >  		hwpt_paging = iommufd_hwpt_paging_alloc(ucmd->ictx, ioas, idev,
> > > 
> > > ?? What is this?
> > > 
> > > Ah something went wrong earlier in "iommu: Pass in parent domain with
> > > user_data to domain_alloc_user op"
> > > 
> > > Once we added the user_data we should flow it through to the op
> > > always.
> > 
> > Hmm, iommufd_hwpt_paging_alloc doesn't take (or need) user_data,
> > but we could pass in a dummy one if that looks better?
> 
> The point is for the user_data to always be available, the driver
> needs to check it if it is passed.
> 
> This should all be plumbed to allow drivers to also customize their
> paging domains too.

We don't have a use case of customizing the paging domains.
And our selftest isn't covering this path. Nor the case is
supported by the uAPI:

458- * A kernel-managed HWPT will be created with the mappings from the given
459- * IOAS via the @pt_id. The @data_type for this allocation must be set to
460: * IOMMU_HWPT_DATA_NONE. The HWPT can be allocated as a parent HWPT for a
461- * nesting configuration by passing IOMMU_HWPT_ALLOC_NEST_PARENT via @flags.
462- *


Also, if we do passing in the data, we'd need to...

280-static struct iommu_domain *
281-mock_domain_alloc_user(struct device *dev, u32 flags,
282-		       struct iommu_domain *parent,
283:		       const struct iommu_user_data *user_data)
284-{
285-	struct mock_iommu_domain *mock_parent;
286-	struct iommu_hwpt_selftest user_cfg;
287-	int rc;
288-
289:	if (!user_data) {	/* must be mock_domain */

...change this to if (!parent)...

290-		struct mock_dev *mdev = container_of(dev, struct mock_dev, dev);
291-		bool has_dirty_flag = flags & IOMMU_HWPT_ALLOC_DIRTY_TRACKING;
292-		bool no_dirty_ops = mdev->flags & MOCK_FLAGS_DEVICE_NO_DIRTY;
293-
294-		if (parent)
295-			return ERR_PTR(-EINVAL);

...and drop this.

296-		if (has_dirty_flag && no_dirty_ops)
297-			return ERR_PTR(-EOPNOTSUPP);
298-		return __mock_domain_alloc_paging(IOMMU_DOMAIN_UNMANAGED,
299-						  has_dirty_flag);
300-	}
301-
302-	/* must be mock_domain_nested */
303:	if (user_data->type != IOMMU_HWPT_DATA_SELFTEST)
304-		return ERR_PTR(-EOPNOTSUPP);

Thanks
Nicolin