[Intel-gfx] [PATCH] drm/i915: Do not drop pagetables when empty

[Daniel Vetter]

From: Chris Wilson <chris at chris-wilson.co.uk>

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_debugfs.c   |    2 +-
 drivers/gpu/drm/i915/i915_gem_evict.c |   12 +-
 drivers/gpu/drm/i915/i915_gem_gtt.c   | 2017 ++++++++++++++-------------------
 drivers/gpu/drm/i915/i915_gem_gtt.h   |  123 +-
 drivers/gpu/drm/i915/i915_trace.h     |  104 --
 drivers/gpu/drm/i915/i915_vgpu.c      |    9 +-
 drivers/gpu/drm/i915/i915_vma.c       |    9 -
 drivers/gpu/drm/i915/intel_lrc.c      |    4 +-
 8 files changed, 946 insertions(+), 1334 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>
---
 drivers/gpu/drm/i915/i915_gem_gtt.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 96e45a4d5441..4f581adf2fcf 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -755,10 +755,6 @@ static bool gen8_ppgtt_clear_pt(struct i915_address_space *vm,
 	GEM_BUG_ON(pte_end > GEN8_PTES);
 
 	bitmap_clear(pt->used_ptes, pte, num_entries);
-	if (USES_FULL_PPGTT(vm->i915)) {
-		if (bitmap_empty(pt->used_ptes, GEN8_PTES))
-			return true;
-	}
 
 	pt_vaddr = kmap_px(pt);
 
@@ -798,9 +794,6 @@ static bool gen8_ppgtt_clear_pd(struct i915_address_space *vm,
 		}
 	}
 
-	if (bitmap_empty(pd->used_pdes, I915_PDES))
-		return true;
-
 	return false;
 }
 
@@ -829,9 +822,6 @@ static bool gen8_ppgtt_clear_pdp(struct i915_address_space *vm,
 
 	mark_tlbs_dirty(ppgtt);
 
-	if (bitmap_empty(pdp->used_pdpes, I915_PDPES_PER_PDP(dev_priv)))
-		return true;
-
 	return false;
 }
 
-- 
2.11.0