linux-kernel - Re: [PATCH v8 1/1] vfio/nvgpu: Add vfio pci variant module for grace hopper

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Date:   Thu, 7 Sep 2023 21:34:41 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     ankita@...dia.com, yishaih@...dia.com,
        shameerali.kolothum.thodi@...wei.com, kevin.tian@...el.com,
        aniketa@...dia.com, cjia@...dia.com, kwankhede@...dia.com,
        targupta@...dia.com, vsethi@...dia.com, acurrid@...dia.com,
        apopple@...dia.com, jhubbard@...dia.com, danw@...dia.com,
        anuaggarwal@...dia.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v8 1/1] vfio/nvgpu: Add vfio pci variant module for grace
 hopper

On Thu, Sep 07, 2023 at 01:55:46PM -0600, Alex Williamson wrote:

> There's perhaps an argument whether userspace should compose this
> device itself, for example finding the firmware attributes in sysfs and
> directly mmap'ing the coherent memory via /dev/mem to back a virtual
> BAR or otherwise pass-through this associated region.  

I don't think this works, secure boot turns off /dev/mem and other
things that would let you do this AFAIK.

> I've previously raised the point whether the coherent region here
> might be exposed as a device specific region (such as we do for the
> above IGD regions) rather than a virtual BAR, but the NVIDIA folks feel
> strongly that the BAR approach is correct.

I think it really depends on what the qemu side wants to do..

> Please continue the discussion, but I'm not seeing anything here that
> feels significantly different than what we created vfio-pci variant
> drivers to do.

Right, the driver seems fine for what the infrastructure was created
to do.

Jason