Re: [PATCH] drm/pagemap: Guard HPAGE_PMD_ORDER use with CONFIG_ARCH_ENABLE_THP_MIGRATION

["Ghimiray, Himal Prasad" <himal.prasad.ghimiray@intel.com>]

On 22-07-2026 04:02, Matthew Brost wrote:
> HPAGE_PMD_SHIFT expands to BUILD_BUG() when CONFIG_PGTABLE_HAS_HUGE_LEAVES
> is not set, causing a compile error when both CONFIG_TRANSPARENT_HUGEPAGE
> and CONFIG_HUGETLB_PAGE are disabled:
> 
>   drivers/gpu/drm/drm_pagemap.c:480:12: error: call to '__compiletime_assert_458'
>   declared with 'error' attribute: BUILD_BUG failed
>     480 |                         order = HPAGE_PMD_ORDER;
>         |                                 ^
>   include/linux/huge_mm.h:117:26: note: expanded from macro 'HPAGE_PMD_ORDER'
>     117 | #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
>         |                          ^
>   include/linux/huge_mm.h:113:28: note: expanded from macro 'HPAGE_PMD_SHIFT'
>     113 | #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
> 
> Define DRM_PAGEMAP_PMD_ORDER, which maps to HPAGE_PMD_ORDER when
> CONFIG_ARCH_ENABLE_THP_MIGRATION is enabled and to -1 otherwise.
> 
> This is safe because all code paths that use DRM_PAGEMAP_PMD_ORDER are
> reachable only when CONFIG_ARCH_ENABLE_THP_MIGRATION is enabled.
> 
> Fixes: 139ab31aea8a ("drm/pagemap: Correct cpages calculation for migrate_vma_setup")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/r/202607201914.LpAGsbXs-lkp@intel.com/
> Cc: Jan Stancek <jstancek@redhat.com>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>

Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>

> ---
>   drivers/gpu/drm/drm_pagemap.c | 13 ++++++++++---
>   1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
> index 15c78eca180b..951cd92c930c 100644
> --- a/drivers/gpu/drm/drm_pagemap.c
> +++ b/drivers/gpu/drm/drm_pagemap.c
> @@ -12,6 +12,12 @@
>   #include <drm/drm_pagemap_util.h>
>   #include <drm/drm_print.h>
>   
> +#if IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION)
> +#define DRM_PAGEMAP_PMD_ORDER	HPAGE_PMD_ORDER
> +#else
> +#define DRM_PAGEMAP_PMD_ORDER	(-1)
> +#endif
> +
>   /**
>    * DOC: Overview
>    *
> @@ -579,7 +585,7 @@ static int drm_pagemap_cpages(unsigned long *migrate_pfn, unsigned long npages)
>   			order = folio_order(folio);
>   			cpages += NR_PAGES(order);
>   		} else if (migrate_pfn[i] & MIGRATE_PFN_COMPOUND) {
> -			order = HPAGE_PMD_ORDER;
> +			order = DRM_PAGEMAP_PMD_ORDER;
>   			cpages += NR_PAGES(order);
>   		}
>   
> @@ -765,10 +771,11 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
>   
>   		if (migrate.src[i] & MIGRATE_PFN_COMPOUND) {
>   			drm_WARN_ONCE(dpagemap->drm, src_page &&
> -				      folio_order(page_folio(src_page)) != HPAGE_PMD_ORDER,
> +				      folio_order(page_folio(src_page)) !=
> +				      DRM_PAGEMAP_PMD_ORDER,
>   				      "Unexpected folio order\n");
>   
> -			order = HPAGE_PMD_ORDER;
> +			order = DRM_PAGEMAP_PMD_ORDER;
>   			migrate.dst[i] |= MIGRATE_PFN_COMPOUND;
>   
>   			for (j = 1; j < NR_PAGES(order) && i + j < npages; j++)