Re: [PATCH v5 7/9] iommufd: Associate fault object with iommufd_hw_pgtable

[Baolu Lu]

On 5/20/24 11:39 AM, Tian, Kevin wrote:
> > From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Monday, May 20, 2024 10:19 AM
> >
> > On 5/15/24 4:50 PM, Tian, Kevin wrote:
> > > > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > > > Sent: Tuesday, April 30, 2024 10:57 PM
> > > >
> > > > @@ -308,6 +314,19 @@ int iommufd_hwpt_alloc(struct iommufd_ucmd
> > > > *ucmd)
> > > >    		goto out_put_pt;
> > > >    	}
> > > >
> > > > +	if (cmd->flags & IOMMU_HWPT_FAULT_ID_VALID) {
> > > > +		struct iommufd_fault *fault;
> > > > +
> > > > +		fault = iommufd_get_fault(ucmd, cmd->fault_id);
> > > > +		if (IS_ERR(fault)) {
> > > > +			rc = PTR_ERR(fault);
> > > > +			goto out_hwpt;
> > > > +		}
> > > > +		hwpt->fault = fault;
> > > > +		hwpt->domain->iopf_handler = iommufd_fault_iopf_handler;
> > > > +		hwpt->domain->fault_data = hwpt;
> > > > +	}
> > >
> > > this is nesting specific. why not moving it to the nested_alloc()?
> >
> > Nesting is currently a use case for userspace I/O page faults, but this
> > design should be general enough to support other scenarios as well.
>
> Do we allow user page table w/o nesting?
>
> What would be a scenario in which the user doesn't manage the
> page table but still want to handle the I/O page fault? The fault
> should always be delivered to the owner managing the page table...

I am not sure. But if nesting is the only case for user page table, it's
fine to move above code to the nested_alloc helper.

Best regards,
baolu