linux-kernel - Re: [PATCH v4 29/32] vfio-pci/zdev: add DTSM to clp group capability

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Date:   Mon, 14 Mar 2022 18:49:28 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, alex.williamson@...hat.com,
        cohuck@...hat.com, schnelle@...ux.ibm.com, farman@...ux.ibm.com,
        pmorel@...ux.ibm.com, borntraeger@...ux.ibm.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com, gerald.schaefer@...ux.ibm.com,
        agordeev@...ux.ibm.com, svens@...ux.ibm.com, frankja@...ux.ibm.com,
        david@...hat.com, imbrenda@...ux.ibm.com, vneethv@...ux.ibm.com,
        oberpar@...ux.ibm.com, freude@...ux.ibm.com, thuth@...hat.com,
        pasic@...ux.ibm.com, joro@...tes.org, will@...nel.org,
        pbonzini@...hat.com, corbet@....net, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 29/32] vfio-pci/zdev: add DTSM to clp group capability

On Mon, Mar 14, 2022 at 03:44:48PM -0400, Matthew Rosato wrote:
> The DTSM, or designation type supported mask, indicates what IOAT formats
> are available to the guest.  For an interpreted device, userspace will not
> know what format(s) the IOAT assist supports, so pass it via the
> capability chain.  Since the value belongs to the Query PCI Function Group
> clp, let's extend the existing capability with a new version.

Why is this on the VFIO device?

Maybe I don't quite understand it right, but the IOAT is the
'userspace page table'?

That is something that should be modeled as a nested iommu domain.

Querying the formats and any control logic for this should be on the
iommu side not built into VFIO.

Jason