Re: [RFC] iommufd: Use accurate dev_id in the PRI forwarding path

[Baolu Lu <baolu.lu@linux.intel.com>]

On 3/6/25 12:10, Tian, Kevin wrote:
>> From: Liu, Yi L <yi.l.liu@intel.com>
>> Sent: Thursday, March 6, 2025 11:30 AM
>>
>> On 2025/3/6 11:10, Tian, Kevin wrote:
>>>> From: Jason Gunthorpe <jgg@nvidia.com>
>>>> Sent: Thursday, March 6, 2025 1:19 AM
>>>>
>>>> I'm confused about how that can even work if the RID is erased in the
>>>> fabric, how do we deliver the PRI response to the correct entity?
>>>>
>>
>> If the RID is detached, kernel should response any pending PRIs. If user
>> sends a response, it won't suit any pending PRI then dropped.
>>
> 
> Jason talked about the case where the iommu group is created e.g
> for a legacy PCI bridge, with all devices behind sharing a same RID.
> Then there is no way to know which device should receive the response.

The PCI spec requires,

"It (ATS) is permitted to be implemented by Endpoints or RCiEPs."

... but DMA aliases could also be created by pci_add_dma_alias().

Thanks,
baolu