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

[Eric Blau <eblau@eblau.com>]

Can the following patch please be included in the next stable release?
It looks like it was submitted previously by Daniel Vetter, but has not
been included in 4.11.y yet. Thanks.


>From 64b1d89f358df34701d92471b65f99f4eff1b384 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu, 18 May 2017 11:00:15 +0100
Subject: [PATCH] drm/i915: Do not drop pagetables when empty
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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@chris-wilson.co.uk>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v4.10+
---
 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;
 }