linux-kernel - Re: [PATCH 14/29] drm/i915/gvt: devirtualize ->{get,put}_vfio

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Message-ID: <20211102161211.GT2744544@nvidia.com>
Date:   Tue, 2 Nov 2021 13:12:11 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        intel-gfx@...ts.freedesktop.org,
        intel-gvt-dev@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 14/29] drm/i915/gvt: devirtualize ->{get,put}_vfio_device

On Tue, Nov 02, 2021 at 08:05:46AM +0100, Christoph Hellwig wrote:
> Just open code the calls to the VFIO APIs.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
>  drivers/gpu/drm/i915/gvt/dmabuf.c    | 12 ++++++-----
>  drivers/gpu/drm/i915/gvt/hypercall.h |  2 --
>  drivers/gpu/drm/i915/gvt/kvmgt.c     | 22 --------------------
>  drivers/gpu/drm/i915/gvt/mpt.h       | 30 ----------------------------
>  4 files changed, 7 insertions(+), 59 deletions(-)

I suspect the use of get/put here is very questionable

It only prevents the vfio_device from becoming unregistered, but the
main thing a mdev should care about is if it is still beween
opne_device() / close_device() - ie the FD is open, there is a SW
IOMMU available, and memory pins can be made.

Still, not for this patch

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason