[PATCH v4 2/3] drm/gpusvm: do not route system pages to device_unmap() on IOVA unmap

[Honglei Huang <honghuan@amd.com>]

In a mixed range: ctx->allow_mixed dpagemap is not NULL while some entries
are system pages. The unmap loop used:

        dma_unmap_page(...);
    else if (dpagemap && dpagemap->ops->device_unmap)
        dpagemap->ops->device_unmap(...);

When use_iova is true the first condition is false for system pages,
so they fall through to device_unmap() and a system DMA address is
handed to the device specific unmap callback, risking invalid accesses
or state corruption.

Key the branch off addr->proto instead: system pages only need an explicit
dma_unmap_page() in the non IOVA case, IOVA system pages are already torn
down by the single dma_iova_destroy(), and only genuine device pages
reach device_unmap().

This issue was found by Sashiko AI review.

Fixes: 37ad039fb367 ("drm/gpusvm: Use dma-map IOVA alloc, link, and sync API in GPU SVM")
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 | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
index 3145d55cd86..44bb19658dd 100644
--- a/drivers/gpu/drm/drm_gpusvm.c
+++ b/drivers/gpu/drm/drm_gpusvm.c
@@ -1163,12 +1163,18 @@ static void __drm_gpusvm_unmap_pages(struct drm_gpusvm *gpusvm,
 		for (i = 0, j = 0; i < npages; j++) {
 			struct drm_pagemap_addr *addr = &svm_pages->dma_addr[j];
 
-			if (!use_iova && addr->proto == DRM_INTERCONNECT_SYSTEM)
-				dma_unmap_page(dev,
-					       addr->addr,
-					       PAGE_SIZE << addr->order,
-					       addr->dir);
-			else if (dpagemap && dpagemap->ops->device_unmap)
+			if (addr->proto == DRM_INTERCONNECT_SYSTEM) {
+				/*
+				 * Linked IOVA pages were already torn down by
+				 * the dma_iova_unlink()/dma_iova_free() above;
+				 * only the non-IOVA mappings need unmap here.
+				 */
+				if (!use_iova)
+					dma_unmap_page(dev,
+						       addr->addr,
+						       PAGE_SIZE << addr->order,
+						       addr->dir);
+			} else if (dpagemap && dpagemap->ops->device_unmap)
 				dpagemap->ops->device_unmap(dpagemap,
 							    dev, addr);
 			i += 1 << addr->order;
-- 
2.34.1