drm/etnaviv: always flush MMU TLBs on map/unmap

This ensures that the GPU isn't able to write into already freed
objects, as doing this in the IOVA reaper isn't enough, as the
gem_free_object path will also cause unmaps to happen.

On MMUv2 this also ensures that stale entries, which may have
been prefetched into the TLB will be purged.

The flush is low overhead, as it gets batched up with the next
user command buffer, so this isn't incuring an overhead for
each buffer map/unmap.
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>

drivers/gpu/drm/etnaviv/etnaviv_mmu.c

@@ -193,11 +193,8 @@ static int etnaviv_iommu_find_iova(struct etnaviv_iommu *mmu,
 
 		/*
 		 * We removed enough mappings so that the new allocation will
-		 * succeed.  Ensure that the MMU will be flushed before the
-		 * associated commit requesting this mapping, and retry the
-		 * allocation one more time.
+		 * succeed, retry the allocation one more time.
 		 */
-		mmu->need_flush = true;
 	}
 
 	return ret;
@@ -249,6 +246,7 @@ int etnaviv_iommu_map_gem(struct etnaviv_iommu *mmu,
 	}
 
 	list_add_tail(&mapping->mmu_node, &mmu->mappings);
+	mmu->need_flush = true;
 	mutex_unlock(&mmu->lock);
 
 	return ret;
@@ -266,6 +264,7 @@ void etnaviv_iommu_unmap_gem(struct etnaviv_iommu *mmu,
 		etnaviv_iommu_remove_mapping(mmu, mapping);
 
 	list_del(&mapping->mmu_node);
+	mmu->need_flush = true;
 	mutex_unlock(&mmu->lock);
 }