drm/msm: Add modparam to allow vram carveout

Using the GPU with a VRAM Carveout is a security vulnerability.
Nevertheless it is sometimes required, especially when no IOMMU
implementation is available for a certain platform.
Signed-off-by: Iskren Chernev <iskren.chernev@gmail.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/adreno/a2xx_gpu.c

@@ -534,8 +534,10 @@ struct msm_gpu *a2xx_gpu_init(struct drm_device *dev)
 
 	if (!gpu->aspace) {
 		dev_err(dev->dev, "No memory protection without MMU\n");
-		ret = -ENXIO;
-		goto fail;
+		if (!allow_vram_carveout) {
+			ret = -ENXIO;
+			goto fail;
+		}
 	}
 
 	return gpu;

drivers/gpu/drm/msm/adreno/a3xx_gpu.c

@@ -564,8 +564,10 @@ struct msm_gpu *a3xx_gpu_init(struct drm_device *dev)
 		 * implement a cmdstream validator.
 		 */
 		DRM_DEV_ERROR(dev->dev, "No memory protection without IOMMU\n");
-		ret = -ENXIO;
-		goto fail;
+		if (!allow_vram_carveout) {
+			ret = -ENXIO;
+			goto fail;
+		}
 	}
 
 	icc_path = devm_of_icc_get(&pdev->dev, "gfx-mem");

drivers/gpu/drm/msm/adreno/a4xx_gpu.c

@@ -692,8 +692,10 @@ struct msm_gpu *a4xx_gpu_init(struct drm_device *dev)
 		 * implement a cmdstream validator.
 		 */
 		DRM_DEV_ERROR(dev->dev, "No memory protection without IOMMU\n");
-		ret = -ENXIO;
-		goto fail;
+		if (!allow_vram_carveout) {
+			ret = -ENXIO;
+			goto fail;
+		}
 	}
 
 	icc_path = devm_of_icc_get(&pdev->dev, "gfx-mem");

drivers/gpu/drm/msm/adreno/adreno_device.c

@@ -18,6 +18,10 @@ bool snapshot_debugbus = false;
 MODULE_PARM_DESC(snapshot_debugbus, "Include debugbus sections in GPU devcoredump (if not fused off)");
 module_param_named(snapshot_debugbus, snapshot_debugbus, bool, 0600);
 
+bool allow_vram_carveout = false;
+MODULE_PARM_DESC(allow_vram_carveout, "Allow using VRAM Carveout, in place of IOMMU");
+module_param_named(allow_vram_carveout, allow_vram_carveout, bool, 0600);
+
 static const struct adreno_info gpulist[] = {
 	{
 		.rev   = ADRENO_REV(2, 0, 0, 0),

drivers/gpu/drm/msm/adreno/adreno_gpu.h

@@ -18,6 +18,7 @@
 #include "adreno_pm4.xml.h"
 
 extern bool snapshot_debugbus;
+extern bool allow_vram_carveout;
 
 enum {
 	ADRENO_FW_PM4 = 0,