As paranoia, we want to ensure that the CPU's PTEs have been revoked for
the object before we return from i915_gem_release_mmap(). This allows us
to rely on there being no outstanding memory accesses and guarantees
serialisation of the code against concurrent access just by calling
i915_gem_release_mmap().
v2: Reduce the mb() into a wmb() following the revoke.
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: "Goel, Akash" <akash.goel@xxxxxxxxx
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
drivers/gpu/drm/i915/i915_gem.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 765efa88db32..b6879d43dd74 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1936,11 +1936,21 @@ out:
void
i915_gem_release_mmap(struct drm_i915_gem_object *obj)
{
+ /* Serialisation between user GTT access and our code depends upon
+ * revoking the CPU's PTE whilst the mutex is held. The next user
+ * pagefault then has to wait until we release the mutex.
+ */
+ lockdep_assert_held(&obj->base.dev->struct_mutex);
+
if (!obj->fault_mappable)
return;
drm_vma_node_unmap(&obj->base.vma_node,
obj->base.dev->anon_inode->i_mapping);
+
+ /* Ensure that the CPU's PTE are revoked before we return */
+ wmb();
+
obj->fault_mappable = false;
}
@@ -3324,9 +3334,6 @@ static void i915_gem_object_finish_gtt(struct drm_i915_gem_object *obj)
if ((obj->base.read_domains & I915_GEM_DOMAIN_GTT) == 0)
return;
- /* Wait for any direct GTT access to complete */
- mb();
-
old_read_domains = obj->base.read_domains;
old_write_domain = obj->base.write_domain;
--
2.8.0.rc3
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