linux-kernel - [PATCH] drm/cma-helper: Set VM

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Message-Id: <1c68be0449aa3217e2bbc898dd8c7426748fc6b8.1629902585.git.robin.murphy@arm.com>
Date:   Wed, 25 Aug 2021 15:43:05 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de
Cc:     airlied@...ux.ie, daniel@...ll.ch, alyssa.rosenzweig@...labora.com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/cma-helper: Set VM_DONTEXPAND for mmap

drm_gem_cma_mmap() cannot assume every implementation of dma_mmap_wc()
will end up calling remap_pfn_range() (which happens to set the relevant
vma flag, among others), so in order to make sure expectations around
VM_DONTEXPAND are met, let it explicitly set the flag like most other
GEM mmap implementations do.

This avoids repeated warnings on a small minority of systems where the
display is behind an IOMMU, and has a simple driver which does not
override drm_gem_cma_default_funcs.

Signed-off-by: Robin Murphy <robin.murphy@....com>
---
 drivers/gpu/drm/drm_gem_cma_helper.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c
index d53388199f34..63e48d98263d 100644
--- a/drivers/gpu/drm/drm_gem_cma_helper.c
+++ b/drivers/gpu/drm/drm_gem_cma_helper.c
@@ -510,6 +510,7 @@ int drm_gem_cma_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
 	 */
 	vma->vm_pgoff -= drm_vma_node_start(&obj->vma_node);
 	vma->vm_flags &= ~VM_PFNMAP;
+	vma->vm_flags |= VM_DONTEXPAND;

 	cma_obj = to_drm_gem_cma_obj(obj);

-- 
2.25.1