Re: [PATCH v3 05/18] dmaengine: idxd: add IMS support in base driver

[Thomas Gleixner]

On Wed, Sep 30 2020 at 14:49, Ashok Raj wrote:
>> It is the weirdest thing, IMHO. Intel defined a dvsec cap in their
>> SIOV cookbook, but as far as I can see it serves no purpose at
>> all.
>> 
>> Last time I asked I got some unclear mumbling about "OEMs".
>> 
> One of the parameters it has is the "supported system page-sizes" which is
> usually there in the SRIOV properties. So it needed a place holder for
> that. 
>
> IMS is a device specific capability, and I almost forgot why we needed
> until I had to checking internally. Remember when a device is given to a
> guest, MSIX routing via Interrupt Remapping is automatic via the VFIO/IRQFD
> and such.

-ENOPARSE

> When we provision an entire PCI device that is IMS capable. The guest
> driver does know it can update the IMS entries directly without going to
> the host. But in order to do remapping we need something like how we manage
> PASID allocation from guest, so an IRTE entry can be allocated and the host
> driver can write the proper values for IMS.

And how is that related to that capbility thing?

Also this stuff is host side and not guest side. I seriously doubt that
you want to hand in the whole PCI device which contains the IMS
thing. The whole point of IMS was as far as I was told that you can
create gazillions of subdevices and have seperate MSI interrupts for
each of them.

Thanks,

        tglx