Semantic conflict between 04b177544a04 in drm-misc-fixes and 0b6b1bb28482 in -mm

[Nathan Chancellor <nathan@kernel.org>]

Hi Mark and drm and mm folks,

There is a semantic conflict between commit 04b177544a04 ("drm/pagemap:
Guard HPAGE_PMD_ORDER use with CONFIG_ARCH_ENABLE_THP_MIGRATION") in the
drm-misc-fixes tree and commit 0b6b1bb28482 ("mm: rename
ARCH_ENABLE_THP_MIGRATION to ARCH_HAS_PMD_SOFTLEAVES"), resulting in a
lone instance of CONFIG_ARCH_ENABLE_THP_MIGRATION with no way to define
it.

  $ git grep ARCH_ENABLE_THP_MIGRATION
  Next/merge.log:Merging drm-misc-fixes/for-linux-next-fixes (04b177544a040 drm/pagemap: Guard HPAGE_PMD_ORDER use with CONFIG_ARCH_ENABLE_THP_MIGRATION)
  drivers/gpu/drm/drm_pagemap.c:#if IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION)

This results in an objtool warning (or error with CONFIG_OBJTOOL_WERROR)
when building with clang because NR_PAGES(order) results in 1U << -1,
which causes clang to stop generating code for
drm_pagemap_migrate_to_devmem() when encountering unconditional
undefined behavior.

  drivers/gpu/drm/drm_gpusvm_helper.o: error: objtool: drm_pagemap_migrate_to_devmem() falls through to next function drm_pagemap_zdd_alloc()

Mark, could please apply the following diff to the -mm merge to avoid
this? Obviously, there will need to be further coordination for
resolving this upstream when the time comes but it is only an issue in
-next currently.

diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
index 4a794544b7dc..f00c27edbfb9 100644
--- a/drivers/gpu/drm/drm_pagemap.c
+++ b/drivers/gpu/drm/drm_pagemap.c
@@ -12,7 +12,7 @@
 #include <drm/drm_pagemap_util.h>
 #include <drm/drm_print.h>
 
-#if IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION)
+#if IS_ENABLED(CONFIG_ARCH_HAS_PMD_SOFTLEAVES)
 #define DRM_PAGEMAP_PMD_ORDER	HPAGE_PMD_ORDER
 #else
 #define DRM_PAGEMAP_PMD_ORDER	(-1)
-- 
Cheers,
Nathan