Re: Support SVM without PASID

[valmiki <valmikibow@gmail.com>]

On 7/11/2017 1:01 AM, Jerome Glisse wrote:
> On Sun, Jul 09, 2017 at 08:45:57AM +0530, valmiki wrote:
>>>> Hi,
>>>>
>>>> In SMMUv3 architecture document i see "PASIDs are optional,
>>>> configurable, and of a size determined by the minimum
>>>> of the endpoint".
>>>>
>>>> So if PASID's are optional and not supported by PCIe end point, how SVM
>>>> can be achieved ?
>>>
>>> It cannot be inferred from that statement that PASID support is not
>>> required for SVM.  AIUI, SVM is a software feature enabled by numerous
>>> "optional" hardware features, including PASID.  Features that are
>>> optional per the hardware specification may be required for specific
>>> software features.  Thanks,
>>>
>> Thanks for the information Alex. Suppose if an End point doesn't support
>> PASID, is it still possible to achieve SVM ?
>> Are there any such features in SMMUv3 with which we can achieve it ?
>
> You can achieve SVM in software, this is what HMM is for. But the hardware
> must have an mmu with similar features as you get on CPU mmu. Device like
> GPU do have such MMU.
>
> You can also mix HMM with PASID/ATS to leverage device memory. HMM allows
> you to use device memory inside process address space for device threads
> (ie device memory is still consider as un-accessible from CPU, only device
> can access it). Again very useful for GPU.
>
Thanks Jerome, this is interesting and great work. Will try to explore 
more on this option.

Regards,
Valmiki