linux-kernel - [PATCH 5.16 089/227] drm/cma-helper: Set VM

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Date:   Mon, 21 Feb 2022 09:48:28 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>,
        Robin Murphy <robin.murphy@....com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
Subject: [PATCH 5.16 089/227] drm/cma-helper: Set VM_DONTEXPAND for mmap

From: Robin Murphy <robin.murphy@....com>

commit 59f39bfa6553d598cb22f694d45e89547f420d85 upstream.

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.

[Alyssa: Update commit message.]

Fixes: c40069cb7bd6 ("drm: add mmap() to drm_gem_object_funcs")
Acked-by: Daniel Vetter <daniel@...ll.ch>
Signed-off-by: Robin Murphy <robin.murphy@....com>
Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211013143654.39031-1-alyssa@rosenzweig.io
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/drm_gem_cma_helper.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/gpu/drm/drm_gem_cma_helper.c
+++ b/drivers/gpu/drm/drm_gem_cma_helper.c
@@ -518,6 +518,7 @@ int drm_gem_cma_mmap(struct drm_gem_obje
 	 */
 	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);