drm/msm: Limit command submission when no IOMMU

Running the GPU without an IOMMU is not really a supported (or sane)
configuration.  Yet it can be useful during SoC bringup (ie. if the
iommu driver doesn't work yet).

Lets limit it to users who already have /dev/mem access, to avoid the
chance that a user accidentially configures kernel without IOMMU
support.
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20220502172908.3569799-1-robdclark@gmail.comSigned-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/msm_gem_submit.c

@@ -734,6 +734,11 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
 	if (args->pad)
 		return -EINVAL;
 
+	if (unlikely(!ctx->aspace) && !capable(CAP_SYS_RAWIO)) {
+		DRM_ERROR_RATELIMITED("IOMMU support or CAP_SYS_RAWIO required!\n");
+		return -EPERM;
+	}
+
 	/* for now, we just have 3d pipe.. eventually this would need to
 	 * be more clever to dispatch to appropriate gpu module:
 	 */