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

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

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>
---
 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++)
-- 
2.34.1