ACK: [PATCH] drm/i915: Do not drop pagetables when empty

[Seth Forshee]

On Thu, Jul 27, 2017 at 07:05:56PM +0800, Rex Tsai (蔡志展) wrote:
> From: Chris Wilson <chris at chris-wilson.co.uk>
> 
> From: Chris Wilson <chris at chris-wilson.co.uk>
> 
> BugLink: https://bugs.launchpad.net/bugs/1680904
> 
> This is the minimal backport for stable of the upstream commit:
> 
> commit dd19674bacba227ae5d3ce680cbc5668198894dc
> Author: Chris Wilson <chris at chris-wilson.co.uk>
> Date:   Wed Feb 15 08:43:46 2017 +0000
> 
>     drm/i915: Remove bitmap tracking for used-ptes
> 
> Due to a race with the shrinker, when we try to allocate a pagetable, we
> may end up shrinking it instead. This comes as a nasty surprise as we
> try to dereference it to fill in the pagetable entries for the object.
> 
> In linus/master this is fixed by pinning the pagetables prior to
> allocation, but that backport is roughly
>  drivers/gpu/drm/i915/i915_gem_gtt.c |   10 ----------
>  1 file changed, 10 deletions(-)
> i.e. unsuitable for stable. Instead we neuter the code that tried to
> free the pagetables.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99295
> Fixes: 2ce5179fe826 ("drm/i915/gtt: Free unused lower-level page tables")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Michel Thierry <michel.thierry at intel.com>
> Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Michał Winiarski <michal.winiarski at intel.com>
> Cc: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: intel-gfx at lists.freedesktop.org
> Cc: <stable at vger.kernel.org> # v4.10+
> Tested-by: Maël Lavault <mael.lavault at protonmail.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> (cherry picked from commit 92220696d5d07525443d9280c08c498e77d0386c)
> Signed-off-by: Rex Tsai (蔡志展) <rex.tsai at canonical.com>

With the provenance clarification suggested by smb:

Acked-by: Seth Forshee <seth.forshee at canonical.com>