linux-kernel - Re: [PATCH v5 6/9] iommufd: Fault-capable hwpt attach/detach/replace

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Date: Mon, 20 May 2024 10:10:16 +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 6/9] iommufd: Fault-capable hwpt attach/detach/replace

On 5/15/24 4:43 PM, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>> Sent: Tuesday, April 30, 2024 10:57 PM
>> +
>> +int iommufd_fault_domain_replace_dev(struct iommufd_device *idev,
>> +				     struct iommufd_hw_pagetable *hwpt,
>> +				     struct iommufd_hw_pagetable *old)
>> +{
>> +	struct iommu_attach_handle *handle;
>> +	int ret;
>> +
>> +	if (hwpt->fault)
>> +		ret = iommufd_fault_iopf_enable(idev);
>> +	else
>> +		iommufd_fault_iopf_disable(idev);
>> +
>> +	ret = iommu_group_replace_domain(idev->igroup->group, hwpt-
>>> domain);
>> +	if (ret)
>> +		goto out_cleanup;
>> +
>> +	iommufd_auto_response_faults(old, idev);
>> +	handle = iommu_attach_handle_get(idev->igroup->group,
>> IOMMU_NO_PASID, 0);
>> +	handle->idev = idev;
> 
> why is auto response required in replace? new requests can come
> after the auto response anyway...
> 
> The user should prepare for faults delivered to the old or new hwpt
> in the transition window.

The current design of replace allows switching between one that is not
IOPF-capable and one that is. This implies that if we switch from an
IOPF-capable hwpt to a non-IOPF-capable one, the response queue needs to
be auto responded.

Best regards,
baolu