linux-kernel - Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

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Date:   Wed, 31 Mar 2021 09:40:38 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs

On Wed, Mar 31, 2021 at 07:38:36AM +0000, Liu, Yi L wrote:

> The reason is /dev/ioasid FD is per-VM since the ioasid allocated to
> the VM should be able to be shared by all assigned device for the VM.
> But the SVA operations (bind/unbind page table, cache_invalidate) should
> be per-device.

It is not *per-device* it is *per-ioasid*

And as /dev/ioasid is an interface for controlling multiple ioasid's
there is no issue to also multiplex the page table manipulation for
multiple ioasids as well.

What you should do next is sketch out in some RFC the exactl ioctls
each FD would have and show how the parts I outlined would work and
point out any remaining gaps.

The device FD is something like the vfio_device FD from VFIO, it has
*nothing* to do with PASID beyond having a single ioctl to authorize
the device to use the PASID. All control of the PASID is in
/dev/ioasid.

Jason