linux-kernel - Re: [PATCH RFC v2 00/18] Add VFIO mediated device support and DEV-MSI support for the idxd driver

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Message-ID: <20200724001930.GS2021248@mellanox.com>
Date:   Thu, 23 Jul 2020 21:19:30 -0300
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     "Jiang, Dave" <dave.jiang@...el.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "Dey, Megha" <megha.dey@...el.com>,
        "maz@...nel.org" <maz@...nel.org>,
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        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
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        "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>,
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        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH RFC v2 00/18] Add VFIO mediated device support and
 DEV-MSI support for the idxd driver

On Tue, Jul 21, 2020 at 11:54:49PM +0000, Tian, Kevin wrote:
> In a nutshell, applications don't require raw WQ controllability as guest
> kernel drivers may expect. Extending DSA user space interface to be another
> passthrough interface just for virtualization needs is less compelling than
> leveraging established VFIO/mdev framework (with the major merit that
> existing user space VMMs just work w/o any change as long as they already
> support VFIO uAPI).

Sure, but the above is how the cover letter should have summarized
that discussion, not as "it is not much code difference"

> In last review you said that you didn't hard nak this approach and would
> like to hear opinion from virtualization guys. In this version we CCed KVM
> mailing list, Paolo (VFIO/Qemu), Alex (VFIO), Samuel (Rust-VMM/Cloud
> hypervisor), etc. Let's see how they feel about this approach.

Yes, the VFIO community should decide.

If we are doing emulation tasks in the kernel now, then I can think of
several nice semi-emulated mdevs to propose.

This will not be some one off, but the start of a widely copied
pattern.

Jason