FAILED: patch "[PATCH] drm/ttm: return an error when kmapping a BO without pages" failed to apply to 6.1-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x fd485d47437ba1700dd47205a63b9f389a00aa36
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107054617-failed-6.1-fd485d47437b@kernel.org' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From fd485d47437ba1700dd47205a63b9f389a00aa36 Mon Sep 17 00:00:00 2001
From: Jesse Zhang <Jesse.Zhang@amd.com>
Date: Fri, 9 Oct 2026 18:33:39 +0800
Subject: [PATCH] drm/ttm: return an error when kmapping a BO without pages
MIME-Version: 1.0
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Content-Transfer-Encoding: 8bit

ttm_tt objects for imported sg tables (ttm_bo_type_sg, set up by
ttm_sg_tt_init() with TTM_TT_FLAG_EXTERNAL) only have DMA addresses and
no pages array. ttm_bo_kmap() and ttm_bo_vmap() still dereference
ttm->pages for them, so a driver that tries to CPU map such a BO oopses
instead of getting an error:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  RIP: 0010:ttm_bo_kmap+0x26c/0x300 [ttm]
  Call Trace:
   amdgpu_bo_kmap+0x89/0xb0 [amdgpu]
   amdgpu_userq_fence_read_wptr+0x116/0x170 [amdgpu]
   amdgpu_userq_signal_ioctl+0x3fe/0xbb0 [amdgpu]

Return -EINVAL in that case, like ttm_bo_kmap_try_from_panic() already
checks for a missing pages array.

Fixes: 75a57669cbc8 ("drm/ttm: add ttm_sg_tt_init")
Cc: stable@vger.kernel.org
Suggested-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Jesse Zhang <Jesse.Zhang@amd.com>
Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Link: https://patch.msgid.link/20261009103419.4122940-1-Jesse.Zhang@amd.com
---
 drivers/gpu/drm/ttm/ttm_bo_util.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index bd0b23ac2cc4b..f9458a4d5a09d 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -356,6 +356,10 @@ static int ttm_bo_kmap_ttm(struct ttm_buffer_object *bo,
 	if (ret)
 		return ret;
 
+	/* Imported sg tables only come with DMA addresses, no pages to map. */
+	if (!ttm->pages)
+		return -EINVAL;
+
 	if (num_pages == 1 && ttm->caching == ttm_cached &&
 	    !(man->use_tt && (ttm->page_flags & TTM_TT_FLAG_DECRYPTED))) {
 		/*
@@ -419,7 +423,7 @@ EXPORT_SYMBOL(ttm_bo_kmap_try_from_panic);
  *
  * Returns
  * -ENOMEM: Out of memory.
- * -EINVAL: Invalid range.
+ * -EINVAL: Invalid range or the BO has no pages to map.
  */
 int ttm_bo_kmap(struct ttm_buffer_object *bo,
 		unsigned long start_page, unsigned long num_pages,
@@ -493,7 +497,7 @@ EXPORT_SYMBOL(ttm_bo_kunmap);
  *
  * Returns
  * -ENOMEM: Out of memory.
- * -EINVAL: Invalid range.
+ * -EINVAL: Invalid range or the BO has no pages to map.
  */
 int ttm_bo_vmap(struct ttm_buffer_object *bo, struct iosys_map *map)
 {
@@ -537,6 +541,9 @@ int ttm_bo_vmap(struct ttm_buffer_object *bo, struct iosys_map *map)
 		if (ret)
 			return ret;
 
+		if (!ttm->pages)
+			return -EINVAL;
+
 		/*
 		 * We need to use vmap to get the desired page protection
 		 * or to make the buffer object look contiguous.
-- 
2.53.0