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

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Message-ID: <20221206140002.GB27689@lst.de>
Date:   Tue, 6 Dec 2022 15:00:02 +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 09:52:54AM -0400, Jason Gunthorpe wrote:
> On Tue, Dec 06, 2022 at 02:09:01PM +0100, Christoph Hellwig wrote:
> > 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?
> 
> "Requester ID" - PCI SIG term that in Linux basically means you get to
> assign an iommu_domain to the vfio device.

Yeah I now the Requester ID, I've just never seen that shortcut for it.

> >From what I understood this series basically allows two Intel devices
> to pass a big opaque blob of data. Intel didn't document what is in
> that blob, so I assume it captures everything you mention above.

Which would be just as bad, because it then changes the IDs under
the live OS on a restore.  This is not something that can be done
behind the back of the hypervisors / control plane OS.