Re: Support SVM without PASID

[valmiki <valmikibow@gmail.com>]

On 7/11/2017 4:26 PM, Jean-Philippe Brucker wrote:
> Hi Valmiki,
>
> On 09/07/17 04:15, 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 ?
>
> Not really, we don't plan to share the non-PASID context with a process.
>
> In theory you could achieve something resembling SVM by assigning the
> entire endpoint to userspace using VFIO, then use ATS+PRI capabilities
> with a bind ioctl. If your device can do SR-IOV, then you can bind one
> process per virtual function.
>
> Unless we end up seeing lots of endpoints that implement PRI but not
> PASID, I don't plan to add this to VFIO or SMMUv3.
>
> For a PCIe endpoint, the requirements for SVM are ATS, PRI and PASID
> enabled. In addition, the SMMU should support DVM (broadcast TLB
> maintenance) and must be compatible with the MMU (page sizes, output
> address size, ASID bits...)
>
Thanks Jean.
In SMMU document it was quoted as follows
"When STE.S1DSS==0b10, a transaction without a SubstreamID is accepted 
and uses the CD of Substream 0. Under this configuration, transactions 
that arrive with SubstreamID 0 are aborted and an event recorded."

Is this mode supported in your previous series of SMMUv3 patches ?
If it is supported is it achieved through VFIO ?

Regards,
Valmiki