linux-kernel - Re: [PATCH] vfio/gvt: fix DRM_I915_GVT dependency on VFIO

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Date:   Thu, 22 Apr 2021 17:51:47 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...nel.org>
Cc:     Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, intel-gvt-dev@...ts.freedesktop.org,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>
Subject: Re: [PATCH] vfio/gvt: fix DRM_I915_GVT dependency on VFIO_MDEV


Cc: gvt list & maintainers

On Thu, 22 Apr 2021, Jason Gunthorpe <jgg@...pe.ca> wrote:
> On Thu, Apr 22, 2021 at 03:35:33PM +0200, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@...db.de>
>> 
>> The Kconfig dependency is incomplete since DRM_I915_GVT is a 'bool'
>> symbol that depends on the 'tristate' VFIO_MDEV. This allows a
>> configuration with VFIO_MDEV=m, DRM_I915_GVT=y and DRM_I915=y that
>> causes a link failure:
>> 
>> x86_64-linux-ld: drivers/gpu/drm/i915/gvt/gvt.o: in function `available_instances_show':
>> gvt.c:(.text+0x67a): undefined reference to `mtype_get_parent_dev'
>> x86_64-linux-ld: gvt.c:(.text+0x6a5): undefined reference to `mtype_get_type_group_id'
>> x86_64-linux-ld: drivers/gpu/drm/i915/gvt/gvt.o: in function `description_show':
>> gvt.c:(.text+0x76e): undefined reference to `mtype_get_parent_dev'
>> x86_64-linux-ld: gvt.c:(.text+0x799): undefined reference to `mtype_get_type_group_id'
>> 
>> Clarify the dependency by specifically disallowing the broken
>> configuration. If VFIO_MDEV is built-in, it will work, but if
>> VFIO_MDEV=m, the i915 driver cannot be built-in here.
>> 
>> Fixes: 07e543f4f9d1 ("vfio/gvt: Make DRM_I915_GVT depend on VFIO_MDEV")
>> Fixes: 9169cff168ff ("vfio/mdev: Correct the function signatures for the mdev_type_attributes")
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>> ---
>>  drivers/gpu/drm/i915/Kconfig | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> Oh kconfig stuff like this makes my head hurt, thanks for finding it
>
> I also can't see an alternative to this ugly thing, besides having the
> i915 guys properly modularize this code someday
>
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
>
> Jason

-- 
Jani Nikula, Intel Open Source Graphics Center