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

[Jan Stancek]

On Tue, Jul 21, 2026 at 9:15 PM Matthew Brost <matthew.brost@xxxxxxxxx> wrote:
>
> 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@xxxxxxxxx>
> > > Closes: https://lore.kernel.org/r/202607201914.LpAGsbXs-lkp@xxxxxxxxx/
> > > Signed-off-by: Jan Stancek <jstancek@xxxxxxxxxx>
> > > ---
> > >  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

Works for me.

Feel free to add:
Tested-by: Jan Stancek <jstancek@xxxxxxxxxx>
if you'll be posting your version.

Thanks,
Jan

>
> 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
> > >
>