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

[Tian, Kevin]

> 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...