drm/i915: Revoke fenced GTT mmapings across GPU reset

The fence registers are clobbered by a GPU reset. If there is concurrent
user access to a fenced region via a GTT mmaping, the access will not be
fenced during the reset (until we restore the fences afterwards). In order
to prevent invalid access during the reset, before we clobber the fences
first we must invalidate the GTT mmapings. Access to the mmap will then
be forced to fault in the page, and in handling the fault, i915_gem_fault()
will take the struct_mutex and wait upon the reset to complete.

v2: Fix up commentary.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99274
Testcase: igt/gem_mmap_gtt/hang
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170104145110.1486-1-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_fence_reg.c b/drivers/gpu/drm/i915/i915_gem_fence_reg.c
index e03983973252..775059e19ab9 100644
--- a/drivers/gpu/drm/i915/i915_gem_fence_reg.c
+++ b/drivers/gpu/drm/i915/i915_gem_fence_reg.c
@@ -367,6 +367,30 @@ i915_vma_get_fence(struct i915_vma *vma)
 }
 
 /**
+ * i915_gem_revoke_fences - revoke fence state
+ * @dev_priv: i915 device private
+ *
+ * Removes all GTT mmappings via the fence registers. This forces any user
+ * of the fence to reacquire that fence before continuing with their access.
+ * One use is during GPU reset where the fence register is lost and we need to
+ * revoke concurrent userspace access via GTT mmaps until the hardware has been
+ * reset and the fence registers have been restored.
+ */
+void i915_gem_revoke_fences(struct drm_i915_private *dev_priv)
+{
+	int i;
+
+	lockdep_assert_held(&dev_priv->drm.struct_mutex);
+
+	for (i = 0; i < dev_priv->num_fence_regs; i++) {
+		struct drm_i915_fence_reg *fence = &dev_priv->fence_regs[i];
+
+		if (fence->vma)
+			i915_gem_release_mmap(fence->vma->obj);
+	}
+}
+
+/**
  * i915_gem_restore_fences - restore fence state
  * @dev_priv: i915 device private
  *