linux-kernel - Re: [RFC PATCH 1/5] nvme-pci: add function nvme_submit_vf_cmd to issue admin commands for VF driver.

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Date:   Wed, 7 Dec 2022 17:38:57 +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 1/5] nvme-pci: add function nvme_submit_vf_cmd to
 issue admin commands for VF driver.

On Wed, Dec 07, 2022 at 11:07:11AM -0400, Jason Gunthorpe wrote:
> > And while that is a fine concept per see, the current incarnation of
> > that is fundamentally broken is it centered around the controlled
> > VM.  Which really can't work.
> 
> I don't see why you keep saying this. It is centered around the struct
> vfio_device object in the kernel, which is definately NOT the VM.

Sorry, I meant VF.  Your continued using of SR-IOV teminology now keeps
confusing my mind so much that I start mistyping things.

> > Even then you need a controlling and a controlled entity.  The
> > controlling entity even in SIOV remains a PCIe function.  The
> > controlled entity might just be a bunch of hardware resoures and
> > a PASID.  Making it important again that all migration is driven
> > by the controlling entity.
> 
> If they are the same driver implementing vfio_device you may be able
> to claim they conceptually exist, but it is pretty artificial to draw
> this kind of distinction inside a single driver.

How are they in this reply?  I can't parse how this even relates to
what I wrote.

> > Also the whole concept that only VFIO can do live migration is
> > a little bogus.  With checkpoint and restart it absolutely
> > does make sense to live migrate a container, and with that
> > the hardware interface (e.g. nvme controller) assigned to it.
> 
> I agree people may want to do this, but it is very unclear how SRIOV
> live migration can help do this.

SRIOV live migration doesn't, because honestly there is no such
thing as "SRIOV" live migration to start with.

> Let alone how to solve the security problems of allow userspace to
> load arbitary FW blobs into a device with potentially insecure DMA
> access..

Any time you assign a PCI device to userspace you might get into that.