linux-kernel - Re: [RFC PATCH 5/5] nvme-vfio: Add a document for the NVMe device

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Date:   Tue, 6 Dec 2022 14:09:01 +0100
From:   Christoph Hellwig <hch@....de>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Christoph Hellwig <hch@....de>, Lei Rao <lei.rao@...el.com>,
        kbusch@...nel.org, axboe@...com, kch@...dia.com, sagi@...mberg.me,
        alex.williamson@...hat.com, cohuck@...hat.com, yishaih@...dia.com,
        shameerali.kolothum.thodi@...wei.com, kevin.tian@...el.com,
        mjrosato@...ux.ibm.com, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, kvm@...r.kernel.org,
        eddie.dong@...el.com, yadong.li@...el.com, yi.l.liu@...el.com,
        Konrad.wilk@...cle.com, stephen@...eticom.com, hang.yuan@...el.com
Subject: Re: [RFC PATCH 5/5] nvme-vfio: Add a document for the NVMe device

On Tue, Dec 06, 2022 at 09:05:05AM -0400, Jason Gunthorpe wrote:
> In this case Intel has a real PCI SRIOV VF to expose to the guest,
> with a full VF RID.

RID?

> The proper VFIO abstraction is the variant PCI
> driver as this series does. We want to use the variant PCI drivers
> because they properly encapsulate all the PCI behaviors (MSI, config
> space, regions, reset, etc) without requiring re-implementation of this
> in mdev drivers.

I don't think the code in this series has any chance of actually
working.  There is a lot of state associated with a NVMe subsystem,
controller and namespace, such as the serial number, subsystem NQN,
namespace uniqueue identifiers, Get/Set features state, pending AENs,
log page content.  Just migrating from one device to another without
capturing all this has no chance of actually working.

> I don't think we know enough about this space at the moment to fix a
> specification to one path or the other, so I hope the TPAR will settle
> on something that can support both models in SW and people can try
> things out.

I've not seen anyone from Intel actually contributing to the live
migration TPAR, which is almost two month old by now.