On Wed, Oct 13, 2021 at 10:36:54AM -0400, Alyssa Rosenzweig wrote:
From: Robin Murphy <robin.murphy@xxxxxxx>
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. Arm hdlcd is an in-tree affected
driver. Out-of-tree, the Apple DCP driver is affected; this fix is
required for DCP to be mainlined.
How/where does this warn?
Also there should be a lot more drivers than
just these two which have an iommu for the display block, so this not
working is definitely a more wide-spread issue.
-Daniel
Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
Reviewed-and-tested-by: Alyssa Rosenzweig <alyssa@xxxxxxxxxxxxx>
---
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);
--
2.30.2