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

[Matthew Brost <matthew.brost@intel.com>]

On Wed, Jul 22, 2026 at 03:56:05PM -0700, Nathan Chancellor wrote:
> Hi Mark and drm and mm folks,
> 

Typically to get drm_pagemap.c to compile on various configs this is
what is needed:

109 #ifdef CONFIG_PGTABLE_HAS_HUGE_LEAVES
110 #define HPAGE_PMD_SHIFT PMD_SHIFT
111 #define HPAGE_PUD_SHIFT PUD_SHIFT
112 #else
113 #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
114 #define HPAGE_PUD_SHIFT ({ BUILD_BUG(); 0; })
115 #endif

So the drm_pagemap.c code could be:

-#if IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION)
+#if IS_ENABLED(CONFIG_PGTABLE_HAS_HUGE_LEAVES)
#define DRM_PAGEMAP_PMD_ORDER        HPAGE_PMD_ORDER
#else
#define DRM_PAGEMAP_PMD_ORDER        (-1)

This Kconfig has been around since 2024:
git format-patch -1 b979db1611a63

Would it be better for everyone for me to change this in the DRM branches?

Matt

> 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