arm64: Fix swiotlb fallback allocation
authorAlexander Graf <>
Mon, 16 Jan 2017 11:46:33 +0000 (12:46 +0100)
committerCatalin Marinas <>
Tue, 17 Jan 2017 11:48:11 +0000 (11:48 +0000)
Commit b67a8b29df introduced logic to skip swiotlb allocation when all memory
is DMA accessible anyway.

While this is a great idea, __dma_alloc still calls swiotlb code unconditionally
to allocate memory when there is no CMA memory available. The swiotlb code is
called to ensure that we at least try get_free_pages().

Without initialization, swiotlb allocation code tries to access io_tlb_list
which is NULL. That results in a stack trace like this:

  Unable to handle kernel NULL pointer dereference at virtual address 00000000
  [<ffff00000845b908>] swiotlb_tbl_map_single+0xd0/0x2b0
  [<ffff00000845be94>] swiotlb_alloc_coherent+0x10c/0x198
  [<ffff000008099dc0>] __dma_alloc+0x68/0x1a8
  [<ffff000000a1b410>] drm_gem_cma_create+0x98/0x108 [drm]
  [<ffff000000abcaac>] drm_fbdev_cma_create_with_funcs+0xbc/0x368 [drm_kms_helper]
  [<ffff000000abcd84>] drm_fbdev_cma_create+0x2c/0x40 [drm_kms_helper]
  [<ffff000000abc040>] drm_fb_helper_initial_config+0x238/0x410 [drm_kms_helper]
  [<ffff000000abce88>] drm_fbdev_cma_init_with_funcs+0x98/0x160 [drm_kms_helper]
  [<ffff000000abcf90>] drm_fbdev_cma_init+0x40/0x58 [drm_kms_helper]
  [<ffff000000b47980>] vc4_kms_load+0x90/0xf0 [vc4]
  [<ffff000000b46a94>] vc4_drm_bind+0xec/0x168 [vc4]

Thankfully swiotlb code just learned how to not do allocations with the FORCE_NO
option. This patch configures the swiotlb code to use that if we decide not to
initialize the swiotlb framework.

Fixes: b67a8b29df ("arm64: mm: only initialize swiotlb when necessary")
Signed-off-by: Alexander Graf <>
CC: Jisheng Zhang <>
CC: Geert Uytterhoeven <>
CC: Konrad Rzeszutek Wilk <>
Signed-off-by: Catalin Marinas <>

index 716d1226ba6925babc28bc6c14dc175e739c7f57..380ebe70509347f8c9329433a625527b65442aa6 100644 (file)
@@ -404,6 +404,8 @@ void __init mem_init(void)
        if (swiotlb_force == SWIOTLB_FORCE ||
            max_pfn > (arm64_dma_phys_limit >> PAGE_SHIFT))
+       else
+               swiotlb_force = SWIOTLB_NO_FORCE;
        set_max_mapnr(pfn_to_page(max_pfn) - mem_map);