linux-kernel - Re: [PATCH v5 7/9] iommufd: Associate fault object with iommufd_hw

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Date: Fri, 24 May 2024 11:24:46 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Baolu Lu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	Nicolin Chen <nicolinc@...dia.com>,
	"Liu, Yi L" <yi.l.liu@...el.com>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Joel Granados <j.granados@...sung.com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"virtualization@...ts.linux-foundation.org" <virtualization@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 7/9] iommufd: Associate fault object with
 iommufd_hw_pgtable

On Mon, May 20, 2024 at 03:39:54AM +0000, Tian, Kevin wrote:
> > From: Baolu Lu <baolu.lu@...ux.intel.com>
> > Sent: Monday, May 20, 2024 10:19 AM
> > 
> > On 5/15/24 4:50 PM, Tian, Kevin wrote:
> > >> From: Lu Baolu <baolu.lu@...ux.intel.com>
> > >> 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...

userspace always manages the page table, either it updates the IOPTE
directly in a nest or it calls iommufd map operations.

Ideally the driver will allow PRI on normal cases, although it will
probably never be used.

Jason