On Wed, May 19, 2021 at 11:12:46PM +0000, Tian, Kevin wrote:

quoted

From: Jason Gunthorpe <jgg@ziepe.ca>
Sent: Thursday, May 20, 2021 2:07 AM

On Wed, May 19, 2021 at 04:23:21PM +0100, Robin Murphy wrote:

quoted

On 2021-05-17 16:35, Joerg Roedel wrote:

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On Mon, May 17, 2021 at 10:35:00AM -0300, Jason Gunthorpe wrote:

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Well, I'm sorry, but there is a huge other thread talking about the
IOASID design in great detail and why this is all needed. Jumping into
this thread without context and basically rejecting all the
conclusions that were reached over the last several weeks is really
not helpful - especially since your objection is not technical.

I think you should wait for Intel to put together the /dev/ioasid uAPI
proposal and the example use cases it should address then you can give
feedback there, with proper context.

Yes, I think the next step is that someone who read the whole thread
writes up the conclusions and a rough /dev/ioasid API proposal, also
mentioning the use-cases it addresses. Based on that we can discuss the
implications this needs to have for IOMMU-API and code.

 From the use-cases I know the mdev concept is just fine. But if there is
a more generic one we can talk about it.

Just to add another voice here, I have some colleagues working on drivers
where they want to use SMMU Substream IDs for a single hardware block

to

quoted

operate on multiple iommu_domains managed entirely within the
kernel.

If it is entirely within the kernel I'm confused how mdev gets
involved? mdev is only for vfio which is userspace.

Just add some background. aux domain is used to support mdev but they
are not tied together. Literally aux domain just implies that there could be 
multiple domains attached to a device then when one of them becomes
the primary all the remaining are deemed as auxiliary. From this angle it
doesn't matter whether the requirement of multiple domains come from
user or kernel.

You can't entirely use aux domain from inside the kernel because you
can't compose it with the DMA API unless you also attach it to some
struct device, and where will the struct device come from?

We already talked about this on the "how to use PASID from the kernel"
thread.

If Robin just wants to use a stream ID from a kernel driver then that
API to make a PASID == RID seems like a better answer for kernel DMA
than aux domains is.

Jason

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