[RFCv2 PATCH 00/36] Process management for IOMMU + SVM for SMMUv3

[Bob Liu]

Hi Jean,

On 2017/10/12 20:55, Jean-Philippe Brucker wrote:
> On 12/10/17 13:05, Yisheng Xie wrote:
> [...]
>>>>> * An iommu_process can be bound to multiple domains, and a domain can have
>>>>>   multiple iommu_process.
>>>> when bind a task to device, can we create a single domain for it? I am thinking
>>>> about process management without shared PT(for some device only support PASID
>>>> without pri ability), it seems hard to expand if a domain have multiple iommu_process?
>>>> Do you have any idea about this?
>>>
>>> A device always has to be in a domain, as far as I know. Not supporting
>>> PRI forces you to pin down all user mappings (or just the ones you use for
>>> DMA) but you should sill be able to share PT. Now if you don't support
>>> shared PT either, but only PASID, then you'll have to use io-pgtable and a
>>> new map/unmap API on an iommu_process. I don't understand your concern
>>> though, how would the link between process and domains prevent this use-case?
>>>
>> So you mean that if an iommu_process bind to multiple devices it should create
>> multiple io-pgtables? or just share the same io-pgtable?
> 
> I don't know to be honest, I haven't thought much about the io-pgtable
> case, I'm all about sharing the mm :)
> 

Sorry to get back to this thread, but traditional DMA_MAP use case may also want to
enable Substreamid/PASID.
As a general framework, you may also consider SubStreamid/Pasid support for dma map/io-pgtable.

We're considering make io-pgtables per SubStreamid/Pasid, but haven't decide put all 
io-pgtables into a single domain or iommu_process.

Thanks,
Liubo

> It really depends on what the user (GPU driver I assume) wants. I think
> that if you're not sharing an mm with the device, then you're trying to
> hide parts of the process to the device, so you'd also want the
> flexibility of having different io-pgtables between devices. Different
> devices accessing isolated parts of the process requires separate io-pgtables.
>