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Date:   Mon, 7 Jun 2021 16:11:26 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Dave Jiang <dave.jiang@intel.com>
Cc:     "Tian, Kevin" <kevin.tian@intel.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Kirti Wankhede <kwankhede@nvidia.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "vkoul@kernel.org" <vkoul@kernel.org>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "Dey, Megha" <megha.dey@intel.com>,
        "Pan, Jacob jun" <jacob.jun.pan@intel.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>, "Lu, Baolu" <baolu.lu@intel.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@intel.com>,
        "Luck, Tony" <tony.luck@intel.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>,
        "eric.auger@redhat.com" <eric.auger@redhat.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "dmaengine@vger.kernel.org" <dmaengine@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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Subject: Re: [PATCH v6 00/20] Add VFIO mediated device support and DEV-MSI
 support for the idxd driver
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On Mon, Jun 07, 2021 at 11:13:04AM -0700, Dave Jiang wrote:

> So in step 1, we 'tag' the wq to be dedicated to guest usage and put the
> hardware wq into enable state. For a dedicated mode wq, we can definitely
> just register directly and skip the mdev step. For a shared wq mode, we can
> have multiple mdev running on top of a single wq. So we need some way to
> create more mdevs. We can either go with the existing established creation
> path by mdev, or invent something custom for the driver as Jason suggested
> to accomodate additional virtual devices for guests. We implemented the mdev
> path originally with consideration of mdev is established and has a known
> interface already.

It sounds like you could just as easially have a 'create new vfio'
file under the idxd sysfs.. Especially since you already have a bus
and dynamic vfio specific things being created on this bus.

Have you gone over this with Dan?

> I think things become more complicated when we go from a dedicated wq to
> shared wq where the relationship of wq : mdev is 1 : 1 goes to 1 : N. Also
> needing to keep a consistent user config experience is desired, especially
> we already have such behavior since kernel 5.6 for host usages. So we really
> need try to avoid doing wq configuration differently just for "mdev" wqs. In
> the case suggested above, we basically just flipped the configuration steps.
> Mdev is first created through mdev sysfs interface. And then the device
> paramters are configured. Where for us, we configure the device parameter
> first, and then create the mdev. But in the end, it's still the hybrid mdev
> setup right?

So you don't even use mdev to configure anything? Yuk.

Jason