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:   Tue, 6 Dec 2022 16:38:11 +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 Tue, Dec 06, 2022 at 11:22:33AM -0400, Jason Gunthorpe wrote:
> > controlled functions (which could very well be, and in some designs
> > are, additional PFs and not VFs) by controlling function.  
> 
> In principle PF vs VF doesn't matter much - the question is really TLP
> labeling. If the spec says RID A is the controlling RID and RID B is
> the guest RID, then it doesn't matter if they have a PF/VF
> relationship or PF/PF relationship.

Yes.  Or in fact if you use PASIDs inside a single function.

> We have locking issues in Linux SW connecting different SW drivers for
> things that are not a PF/VF relationship, but perhaps that can be
> solved.

And I think the only reasonable answer is that the entire workflow
must be 100% managed from the controlling function, and the controlled
function is just around for a ride, with the controlling function
enabling/disabling it as needed without ever interacting with software
that directly deals with the controlled function.