When running vfio_dma_mapping_mmio_test in MODE_IOMMUFD_COMPAT* mode,
the test crashes with "Test terminated unexpectedly by signal 11".

The crash happens because:
1. __iommu_map() fails as expected for MMIO mappings in iommufd.
Consequently, the region.link remains uninitialized.
2. The test proceeds to call __iommu_unmap().
3. In iommufd compat mode, the kernel returns 0 for unmapping a
non-existent range.
4. __iommu_unmap() calls list_del_init(&region->link), dereferencing the
uninitialized pointer.

Fix this by explicitly initializing region.link using INIT_LIST_HEAD.

Signed-off-by: Yi Lai <yi1.lai@intel.com>
---
 tools/testing/selftests/vfio/vfio_dma_mapping_mmio_test.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/vfio/vfio_dma_mapping_mmio_test.c b/tools/testing/selftests/vfio/vfio_dma_mapping_mmio_test.c
index 957a89ce7b3a..4f7ecdca0215 100644
--- a/tools/testing/selftests/vfio/vfio_dma_mapping_mmio_test.c
+++ b/tools/testing/selftests/vfio/vfio_dma_mapping_mmio_test.c
@@ -88,6 +88,7 @@ static void do_mmio_map_test(struct iommu *iommu,
 		.vaddr = vaddr,
 		.size = size,
 		.iova = iova_allocator_alloc(iova_allocator, size),
+		.link = LIST_HEAD_INIT(region.link),
 	};
 
 	/*
-- 
2.43.0