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Message-ID: <a43634c5-4005-4701-8f3e-d4fffcee9193@linux.intel.com>
Date: Mon, 20 May 2024 12:00:39 +0800
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Cc: baolu.lu@linux.intel.com, "iommu@lists.linux.dev"
 <iommu@lists.linux.dev>,
 "virtualization@lists.linux-foundation.org"
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Subject: Re: [PATCH v5 7/9] iommufd: Associate fault object with
 iommufd_hw_pgtable
To: "Tian, Kevin" <kevin.tian@intel.com>, Jason Gunthorpe <jgg@ziepe.ca>,
 Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
 Robin Murphy <robin.murphy@arm.com>,
 Jean-Philippe Brucker <jean-philippe@linaro.org>,
 Nicolin Chen <nicolinc@nvidia.com>, "Liu, Yi L" <yi.l.liu@intel.com>,
 Jacob Pan <jacob.jun.pan@linux.intel.com>,
 Joel Granados <j.granados@samsung.com>
References: <20240430145710.68112-1-baolu.lu@linux.intel.com>
 <20240430145710.68112-8-baolu.lu@linux.intel.com>
 <BN9PR11MB5276A8E898983310B83C399E8CEC2@BN9PR11MB5276.namprd11.prod.outlook.com>
 <b09f96db-8451-4de9-81c5-312cffdfd4fc@linux.intel.com>
 <BN9PR11MB5276F07A130CD617777A3AAD8CE92@BN9PR11MB5276.namprd11.prod.outlook.com>
Content-Language: en-US
From: Baolu Lu <baolu.lu@linux.intel.com>
In-Reply-To: <BN9PR11MB5276F07A130CD617777A3AAD8CE92@BN9PR11MB5276.namprd11.prod.outlook.com>
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On 5/20/24 11:39 AM, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@linux.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@linux.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