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

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

On Tue, Jul 21, 2026 at 12:12:01PM -0700, Matthew Brost wrote:
> On Tue, Jul 21, 2026 at 12:40:38PM +0200, Jan Stancek 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; })
> > 
> > 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;
> 
> Would it be do something like this at the top of the file...
> 
> #ifdef HPAGE_PMD_ORDER
> #define DRM_PAGEMAP_PMD_ORDER	HPAGE_PMD_ORDER
> #else
> #define DRM_PAGEMAP_PMD_ORDER	(-1)
> #endif
> 

Opps screwed my snippet up - HPAGE_PMD_ORDER seems to be always defined...

So actually...

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

Matt

> Then in common code s/HPAGE_PMD_ORDER/DRM_PAGEMAP_PMD_ORDER/
> 
> I think this works as we can never get to the MIGRATE_PFN_COMPOUND code
> paths without CONFIG_ARCH_ENABLE_THP_MIGRATION enabled (see
> mm/migrate_device.c).
> 
> Also btw fixing the unrelated bug Sashiko flagged in this patch.
> 
> Matt
> 
> >  			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
> >