[PATCH v4 3/3] drm/gpusvm: publish dpagemap early to avoid device mapping leak on error

[Honglei Huang <honghuan@amd.com>]

drm_gpusvm_get_pages() only stored the local dpagemap into
svm_pages->dpagemap on the success path. If a later page failed (e.g.
-EOPNOTSUPP when ctx->allow_mixed is false) and jumped to err_unmap,
svm_pages->dpagemap was still NULL, so __drm_gpusvm_unmap_pages() skipped
device_unmap() and leaked the device mappings already created.

Assign svm_pages->dpagemap when the first device page is mapped so the
err_unmap path can device_unmap() those mappings.

This issue was found by Sashiko AI review.

Fixes: f70da6f99d4f ("drm/gpusvm: pull out drm_gpusvm_pages substructure")
Cc: stable@vger.kernel.org
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Honglei Huang <honghuan@amd.com>
---
 drivers/gpu/drm/drm_gpusvm.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
index 44bb19658dd..9a06ff7d260 100644
--- a/drivers/gpu/drm/drm_gpusvm.c
+++ b/drivers/gpu/drm/drm_gpusvm.c
@@ -1544,6 +1544,16 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
 					err = -EAGAIN;
 					goto err_unmap;
 				}
+
+				/*
+				 * Set the dpagemap as soon as the first
+				 * device page is mapped so the err_unmap path
+				 * can device_unmap() the device mappings that
+				 * have already been created.
+				 */
+				drm_pagemap_get(dpagemap);
+				drm_pagemap_put(svm_pages->dpagemap);
+				svm_pages->dpagemap = dpagemap;
 			}
 			svm_pages->dma_addr[j] =
 				dpagemap->ops->device_map(dpagemap,
@@ -1611,12 +1621,8 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
 			goto err_unmap;
 	}
 
-	if (pagemap) {
+	if (pagemap)
 		flags.has_devmem_pages = true;
-		drm_pagemap_get(dpagemap);
-		drm_pagemap_put(svm_pages->dpagemap);
-		svm_pages->dpagemap = dpagemap;
-	}
 
 	/* WRITE_ONCE pairs with READ_ONCE for opportunistic checks */
 	WRITE_ONCE(svm_pages->flags.__flags, flags.__flags);
-- 
2.34.1