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

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Message-ID: <a43634c5-4005-4701-8f3e-d4fffcee9193@linux.intel.com>
Date: Mon, 20 May 2024 12:00:39 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Jason Gunthorpe <jgg@...pe.ca>,
 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>
Cc: baolu.lu@...ux.intel.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 5/20/24 11:39 AM, 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...

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