Re: [RFC] /dev/ioasid uAPI proposal

[Lu Baolu]

Hi Jason W,

On 6/1/21 1:08 PM, Jason Wang wrote:
> > > 2) If yes, what's the reason for not simply use the fd opened from
> > > /dev/ioas. (This is the question that is not answered) and what happens
> > > if we call GET_INFO for the ioasid_fd?
> > > 3) If not, how GET_INFO work?
> > oh, missed this question in prior reply. Personally, no special reason
> > yet. But using ID may give us opportunity to customize the management
> > of the handle. For one, better lookup efficiency by using xarray to
> > store the allocated IDs. For two, could categorize the allocated IDs
> > (parent or nested). GET_INFO just works with an input FD and an ID.
>
>
> I'm not sure I get this, for nesting cases you can still make the child 
> an fd.
>
> And a question still, under what case we need to create multiple ioasids 
> on a single ioasid fd?

One possible situation where multiple IOASIDs per FD could be used is
that devices with different underlying IOMMU capabilities are sharing a
single FD. In this case, only devices with consistent underlying IOMMU
capabilities could be put in an IOASID and multiple IOASIDs per FD could
be applied.

Though, I still not sure about "multiple IOASID per-FD" vs "multiple
IOASID FDs" for such case.

Best regards,
baolu