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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Date:   Tue, 18 Aug 2020 14:18:14 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
CC:     "Tian, Kevin" <kevin.tian@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
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        "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>,
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Subject: Re: [PATCH RFC v2 00/18] Add VFIO mediated device support and
 DEV-MSI support for the idxd driver

On Tue, Aug 18, 2020 at 07:05:16PM +0200, Paolo Bonzini wrote:
> On 18/08/20 18:49, Jason Gunthorpe wrote:
> > On Tue, Aug 18, 2020 at 06:27:21PM +0200, Paolo Bonzini wrote:
> >> On 18/08/20 13:50, Jason Gunthorpe wrote:
> >>> For instance, what about suspend/resume of containers using idxd?
> >>> Wouldn't you want to have the same basic approach of controlling the
> >>> wq from userspace that virtualization uses?
> >>
> >> The difference is that VFIO more or less standardizes the approach you
> >> use for live migration.  With another interface you'd have to come up
> >> with something for every driver, and add support in CRIU for every
> >> driver as well.
> > 
> > VFIO is very unsuitable for use as some general userspace. It only 1:1
> > with a single process and just can't absorb what the existing idxd
> > userspace is doing.
> 
> The point of mdev is that it's not 1:1 anymore.

The lifecycle model of mdev is not compatible with how something like
idxd works, it needs a multi-open cdev.

Jason