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

[Jan Stancek <jstancek@redhat.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; })

Guard the two HPAGE_PMD_ORDER uses with CONFIG_ARCH_ENABLE_THP_MIGRATION,
matching the pattern used in migrate_device.c.

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/
Signed-off-by: Jan Stancek <jstancek@redhat.com>
---
 drivers/gpu/drm/drm_pagemap.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
index 15c78eca180b..53a78752c8be 100644
--- a/drivers/gpu/drm/drm_pagemap.c
+++ b/drivers/gpu/drm/drm_pagemap.c
@@ -578,10 +578,13 @@ static int drm_pagemap_cpages(unsigned long *migrate_pfn, unsigned long npages)
 			folio = page_folio(page);
 			order = folio_order(folio);
 			cpages += NR_PAGES(order);
-		} else if (migrate_pfn[i] & MIGRATE_PFN_COMPOUND) {
+		}
+#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
+		else if (migrate_pfn[i] & MIGRATE_PFN_COMPOUND) {
 			order = HPAGE_PMD_ORDER;
 			cpages += NR_PAGES(order);
 		}
+#endif
 
 		i += NR_PAGES(order);
 	}
@@ -733,7 +736,6 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
 	own_pages = 0;
 
 	for (i = 0; i < npages;) {
-		unsigned long j;
 		struct page *page = pfn_to_page(migrate.dst[i]);
 		struct page *src_page = migrate_pfn_to_page(migrate.src[i]);
 		unsigned int order = 0;
@@ -763,7 +765,10 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
 		}
 		migrate.dst[i] = migrate_pfn(migrate.dst[i]);
 
+#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
 		if (migrate.src[i] & MIGRATE_PFN_COMPOUND) {
+			unsigned long j;
+
 			drm_WARN_ONCE(dpagemap->drm, src_page &&
 				      folio_order(page_folio(src_page)) != HPAGE_PMD_ORDER,
 				      "Unexpected folio order\n");
@@ -774,6 +779,7 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
 			for (j = 1; j < NR_PAGES(order) && i + j < npages; j++)
 				migrate.dst[i + j] = 0;
 		}
+#endif
 
 		drm_pagemap_get_devmem_page(page, order, zdd);
 
-- 
2.52.0