Hi,
On 06/10/15 12:58, Chris Wilson wrote:
As paranoia, we want to ensure that the CPU's PTEs have been revoked for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().
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
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 2b8ed7a2faab..642644f12295 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1877,11 +1877,21 @@ 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 */
+ mb();
+
smp_mb() or smp_wmb() would not suffice? Is it needed on uniprocessor?
Regards,
Tvrtko
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