Re: [PATCH -stable] drm/fb_helper: Allow leaking fbdev smem_start

[Greg KH <greg@kroah.com>]

On Fri, Jan 11, 2019 at 04:06:38PM +0100, Maxime Ripard wrote:
> From: Neil Armstrong <narmstrong@baylibre.com>
> 
> commit 4be9bd10e22dfc7fc101c5cf5969ef2d3a042d8a upstream.
> 
> Since "drm/fb: Stop leaking physical address", the default behaviour of
> the DRM fbdev emulation is to set the smem_base to 0 and pass the new
> FBINFO_HIDE_SMEM_START flag.
> 
> The main reason is to avoid leaking physical addresse to user-space, and
> it follows a general move over the kernel code to avoid user-space to
> manipulate physical addresses and then use some other mechanisms like
> dma-buf to transfer physical buffer handles over multiple subsystems.
> 
> But, a lot of devices depends on closed sources binaries to enable
> OpenGL hardware acceleration that uses this smem_start value to
> pass physical addresses to out-of-tree modules in order to render
> into these physical adresses. These should use dma-buf buffers allocated
> from the DRM display device instead and stop relying on fbdev overallocation
> to gather DMA memory (some HW vendors delivers GBM and Wayland capable
> binaries, but older unsupported devices won't have these new binaries
> and are doomed until an Open Source solution like Lima finalizes).
> 
> Since these devices heavily depends on this kind of software and because
> the smem_start population was available for years, it's a breakage to
> stop leaking smem_start without any alternative solutions.
> 
> This patch adds a Kconfig depending on the EXPERT config and an unsafe
> kernel module parameter tainting the kernel when enabled.
> 
> A clear comment and Kconfig help text was added to clarify why and when
> this patch should be reverted, but in the meantime it's a necessary
> feature to keep.
> 
> Cc: Dave Airlie <airlied@gmail.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> Cc: Noralf Trønnes <noralf@tronnes.org>
> Cc: Maxime Ripard <maxime.ripard@bootlin.com>
> Cc: Eric Anholt <eric@anholt.net>
> Cc: Lucas Stach <l.stach@pengutronix.de>
> Cc: Rob Clark <robdclark@gmail.com>
> Cc: Ben Skeggs <skeggsb@gmail.com>
> Cc: Christian König <christian.koenig@amd.com>
> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
> Reviewed-by: Maxime Ripard <maxime.ripard@bootlin.com>
> Tested-by: Maxime Ripard <maxime.ripard@bootlin.com>
> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Acked-by: Dave Airlie <airlied@gmail.com>
> Link: https://patchwork.freedesktop.org/patch/msgid/1538136355-15383-1-git-send-email-narmstrong@baylibre.com
> Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
> 
> ---
> 
> Hi,
> 
> This is a backport of a patch fixing a regression introduced in 4.19, and
> merged in 4.20. Therefore, it targets 4.19 only.

Now queued up, thanks.

greg k-h