linux-kernel - Re: [PATCH v6 00/20] Add VFIO mediated device support and DEV-MSI support for the idxd driver

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Date:   Thu, 3 Jun 2021 08:23:47 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     "Alex Williamson (alex.williamson@...hat.com)" 
        <alex.williamson@...hat.com>, Cornelia Huck <cohuck@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Dey, Megha" <megha.dey@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Lu, Baolu" <baolu.lu@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v6 00/20] Add VFIO mediated device support and DEV-MSI
 support for the idxd driver

On Thu, Jun 03, 2021 at 05:52:58AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@...dia.com>
> > Sent: Thursday, June 3, 2021 9:50 AM
> > 
> > On Thu, Jun 03, 2021 at 01:11:37AM +0000, Tian, Kevin wrote:
> > 
> > > Jason, can you clarify your attitude on mdev guid stuff? Are you
> > > completely against it or case-by-case? If the former, this is a big
> > > decision thus it's better to have consensus with Alex/Kirti. If the
> > > latter, would like to hear your criteria for when it can be used
> > > and when not...
> > 
> > I dislike it generally, but it exists so <shrug>. I know others feel
> > more strongly about it being un-kernely and the wrong way to use sysfs.
> > 
> > Here I was remarking how the example in the cover letter made the mdev
> > part seem totally pointless. If it is pointless then don't do it.
> 
> Is your point about that as long as a mdev requires pre-config
> through driver specific sysfs then it doesn't make sense to use
> mdev guid interface anymore?

Yes

> The value of mdev guid interface is providing a vendor-agnostic
> interface for mdev life-cycle management which allows one-
> enable-fit-all in upper management stack. Requiring vendor
> specific pre-config does blur the boundary here.

It isn't even vendor-agnostic - understanding the mdev_type
configuration stuff is still vendor specific.

Jason