drm/i915/ttm: handle blitter failure on DG2

If the move or clear operation somehow fails, and the memory underneath
is not cleared, like when moving to lmem, then we currently fallback to
memcpy or memset. However with small-BAR systems this fallback might no
longer be possible. For now we use the set_wedged sledgehammer if we
ever encounter such a scenario, and mark the object as borked to plug
any holes where access to the memory underneath can happen. Add some
basic selftests to exercise this.

v2:
  - In the selftests make sure we grab the runtime pm around the reset.
    Also make sure we grab the reset lock before checking if the device
    is wedged, since the wedge might still be in-progress and hence the
    bit might not be set yet.
  - Don't wedge or put the object into an unknown state, if the request
    construction fails (or similar). Just returning an error and
    skipping the fallback should be safe here.
  - Make sure we wedge each gt. (Thomas)
  - Peek at the unknown_state in io_reserve, that way we don't have to
    export or hand roll the fault_wait_for_idle. (Thomas)
  - Add the missing read-side barriers for the unknown_state. (Thomas)
  - Some kernel-doc fixes. (Thomas)
v3:
  - Tweak the ordering of the set_wedged, also add FIXME.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Jon Bloomfield <jon.bloomfield@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Kenneth Graunke <kenneth@whitecape.org>
Cc: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220629174350.384910-11-matthew.auld@intel.com

1 files changed, 21 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
index 06b1b188ce5a..642a5d59ce26 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
@@ -783,10 +783,31 @@ int i915_gem_object_wait_moving_fence(struct drm_i915_gem_object *obj,
 				    intr, MAX_SCHEDULE_TIMEOUT);
 	if (!ret)
 		ret = -ETIME;
+	else if (ret > 0 && i915_gem_object_has_unknown_state(obj))
+		ret = -EIO;
 
 	return ret < 0 ? ret : 0;
 }
 
+/**
+ * i915_gem_object_has_unknown_state - Return true if the object backing pages are
+ * in an unknown_state. This means that userspace must NEVER be allowed to touch
+ * the pages, with either the GPU or CPU.
+ *
+ * ONLY valid to be called after ensuring that all kernel fences have signalled
+ * (in particular the fence for moving/clearing the object).
+ */
+bool i915_gem_object_has_unknown_state(struct drm_i915_gem_object *obj)
+{
+	/*
+	 * The below barrier pairs with the dma_fence_signal() in
+	 * __memcpy_work(). We should only sample the unknown_state after all
+	 * the kernel fences have signalled.
+	 */
+	smp_rmb();
+	return obj->mm.unknown_state;
+}
+
 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
 #include "selftests/huge_gem_object.c"
 #include "selftests/huge_pages.c"