Re: [PATCH] char/agp: Disable frontend without CONFIG_DRM_LEGACY

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi

Am 18.11.20 um 09:53 schrieb Daniel Vetter:
> On Wed, Nov 18, 2020 at 9:24 AM Christian König
> <christian.koenig@xxxxxxx> wrote:
> > Am 18.11.20 um 09:02 schrieb Thomas Zimmermann:
> > > Hi
> > >
> > > Am 17.11.20 um 22:40 schrieb Daniel Vetter:
> > > > It's probably full of bugs ready for exploiting by userspace. And
> > > > there's not going to be any userspace for this without any of the drm
> > > > legacy drivers enabled too. So just couple it together.
> > > >
> > > > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > > > Cc: David Airlie <airlied@xxxxxxxx>
> > > > Cc: Adam Jackson <ajax@xxxxxxxxxx>
> > > > ---
> > > >    drivers/char/agp/Makefile | 6 +++++-
> > > >    drivers/char/agp/agp.h    | 5 +++++
> > > >    2 files changed, 10 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/char/agp/Makefile b/drivers/char/agp/Makefile
> > > > index cb2497d157f6..90ed8c789e48 100644
> > > > --- a/drivers/char/agp/Makefile
> > > > +++ b/drivers/char/agp/Makefile
> > > > @@ -1,7 +1,11 @@
> > > >    # SPDX-License-Identifier: GPL-2.0
> > > > -agpgart-y := backend.o frontend.o generic.o isoch.o
> > > > +agpgart-y := backend.o generic.o isoch.o
> > > >
> > > > +ifeq ($(CONFIG_DRM_LEGACY),y)
> > > >    agpgart-$(CONFIG_COMPAT)   += compat_ioctl.o
> > > > +agpgart-y                   += frontend.o
> > > > +endif
> > > > +
> > > >
> > > >    obj-$(CONFIG_AGP)          += agpgart.o
> > > >    obj-$(CONFIG_AGP_ALI)              += ali-agp.o
> > > > diff --git a/drivers/char/agp/agp.h b/drivers/char/agp/agp.h
> > > > index 4eb1c772ded7..bb09d64cd51e 100644
> > > > --- a/drivers/char/agp/agp.h
> > > > +++ b/drivers/char/agp/agp.h
> > > > @@ -186,8 +186,13 @@ int agp_add_bridge(struct agp_bridge_data *bridge);
> > > >    void agp_remove_bridge(struct agp_bridge_data *bridge);
> > > >
> > > >    /* Frontend routines. */
> > > > +#if IS_ENABLED(CONFIG_DRM_LEGACY)
> > > >    int agp_frontend_initialize(void);
> > > >    void agp_frontend_cleanup(void);
> > > > +#else
> > > > +static inline int agp_frontend_initialize(void) { return 0; }
> > > > +static inline void agp_frontend_cleanup(void) {}
> > > > +#endif
> > > There's one non-legacy driver that uses these agp structures, which is
> > > radeon. Does this change affect radeon?
> >
> > Nouveau uses AGP as well, but I'm not sure if both drivers use any of
> > this stuff.
>
> frontend = /dev/agp chardev interface for userspace drivers. If you're
> looking at kernel drivers, you're looking at the wrong thing, the
> kernel-internal interface is in char/agp/backend.c and still enabled.
> So no impact at all on any kernel code.
>
> Now the impact this does have on kms drivers using agp is that there's
> no longer a userspace ioctl interface to change the agp setup and
> mappings and fight the kms driver (which assumes it's fully in control
> of agp configuration).

Thanks for clarifying. I'm certainly not qualified, but still

Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>

Best regards
Thomas

> -Daniel
>
> > Regards,
> > Christian.
> >
> > > Best regards
> > > Thomas
> > >
> > > >    /* Generic routines. */
> > > >    void agp_generic_enable(struct agp_bridge_data *bridge, u32 mode);

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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