Re: [PATCH v2 5/5] iommu/vt-d: Move PRI handling to IOPF feature path

Baolu Lu
2023-03-16T08:18:14Z

On 2023/3/16 15:17, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@linux.intel.com>
>> Sent: Thursday, March 9, 2023 10:57 AM
>>
>> @@ -4689,17 +4704,21 @@ static int intel_iommu_disable_iopf(struct device
>> *dev)
>> {
>> struct device_domain_info *info = dev_iommu_priv_get(dev);
>> struct intel_iommu *iommu = info->iommu;
>> - int ret;
>>
>> - ret = iommu_unregister_device_fault_handler(dev);
>> - if (ret)
>> - return ret;
>> + if (!info->pri_enabled)
>> + return -EINVAL;
>>
>> - ret = iopf_queue_remove_device(iommu->iopf_queue, dev);
>> - if (ret)
>> - iommu_register_device_fault_handler(dev,
>> iommu_queue_iopf, dev);
>> + pci_disable_pri(to_pci_dev(dev));
>> + info->pri_enabled = 0;
>>
>> - return ret;
>> + /*
>> + * With pri_enabled checked, unregistering fault handler and
>> + * removing device from iopf queue should never fail.
>> + */
>> + iommu_unregister_device_fault_handler(dev);
>> + iopf_queue_remove_device(iommu->iopf_queue, dev);
>> +
>> + return 0;
>> }
>
> PCIe spec says that clearing the enable bit doesn't mean in-fly
> page requests are completed:
> --
> Enable (E) - This field, when set, indicates that the Page Request
> Interface is allowed to make page requests. If this field is Clear,
> the Page Request Interface is not allowed to issue page requests.
> If both this field and the Stopped field are Clear, then the Page
> Request Interface will not issue new page requests, but has
> outstanding page requests that have been transmitted or are
> queued for transmission

Yes. So the iommu driver should drain the in-fly PRQs.

The Intel VT-d implementation drains the PRQs when any PASID is unbound
from the iommu domain (see intel_svm_drain_prq()) before reuse. Before
disabling iopf, the device driver should unbind pasid and disable sva,
so when it comes here, the PRQ should have been drained.

Perhaps I can add below comments to make this clear:

/*
* PCIe spec states that by clearing PRI enable bit, the Page
* Request Interface will not issue new page requests, but has
* outstanding page requests that have been transmitted or are
* queued for transmission. This is supposed to be called after
* the device driver has stopped DMA, all PASIDs have been
* unbound and the outstanding PRQs have been drained.
*/

Best regards,
baolu