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* [PATCH] drm/cma-helper: Set VM_DONTEXPAND for mmap
@ 2021-08-25 14:43 Robin Murphy
  2021-08-26  1:15 ` Alyssa Rosenzweig
  0 siblings, 1 reply; 2+ messages in thread
From: Robin Murphy @ 2021-08-25 14:43 UTC (permalink / raw)
  To: maarten.lankhorst, mripard, tzimmermann
  Cc: airlied, daniel, alyssa.rosenzweig, dri-devel, linux-kernel

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 <>
 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);

^ permalink raw reply	[flat|nested] 2+ messages in thread

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2021-08-25 14:43 [PATCH] drm/cma-helper: Set VM_DONTEXPAND for mmap Robin Murphy
2021-08-26  1:15 ` Alyssa Rosenzweig

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