Re: Semantic conflict between 04b177544a04 in drm-misc-fixes and 0b6b1bb28482 in -mm

[Nathan Chancellor <nathan@kernel.org>]

On Wed, Jul 22, 2026 at 04:15:49PM -0700, Matthew Brost wrote:
> On Wed, Jul 22, 2026 at 03:56:05PM -0700, Nathan Chancellor wrote:
> > Hi Mark and drm and mm folks,
> > 
> 
> Typically to get drm_pagemap.c to compile on various configs this is
> what is needed:
> 
> 109 #ifdef CONFIG_PGTABLE_HAS_HUGE_LEAVES
> 110 #define HPAGE_PMD_SHIFT PMD_SHIFT
> 111 #define HPAGE_PUD_SHIFT PUD_SHIFT
> 112 #else
> 113 #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
> 114 #define HPAGE_PUD_SHIFT ({ BUILD_BUG(); 0; })
> 115 #endif
> 
> So the drm_pagemap.c code could be:
> 
> -#if IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION)
> +#if IS_ENABLED(CONFIG_PGTABLE_HAS_HUGE_LEAVES)
> #define DRM_PAGEMAP_PMD_ORDER        HPAGE_PMD_ORDER
> #else
> #define DRM_PAGEMAP_PMD_ORDER        (-1)

Ah yeah, I probably should have looked at the bigger picture there.

> This Kconfig has been around since 2024:
> git format-patch -1 b979db1611a63
> 
> Would it be better for everyone for me to change this in the DRM branches?

I believe that would render this conflict moot and seems like the
correct thing to do anyways but you could wait for input from the mm
folks.

> > There is a semantic conflict between commit 04b177544a04 ("drm/pagemap:
> > Guard HPAGE_PMD_ORDER use with CONFIG_ARCH_ENABLE_THP_MIGRATION") in the
> > drm-misc-fixes tree and commit 0b6b1bb28482 ("mm: rename
> > ARCH_ENABLE_THP_MIGRATION to ARCH_HAS_PMD_SOFTLEAVES"), resulting in a
> > lone instance of CONFIG_ARCH_ENABLE_THP_MIGRATION with no way to define
> > it.
> > 
> >   $ git grep ARCH_ENABLE_THP_MIGRATION
> >   Next/merge.log:Merging drm-misc-fixes/for-linux-next-fixes (04b177544a040 drm/pagemap: Guard HPAGE_PMD_ORDER use with CONFIG_ARCH_ENABLE_THP_MIGRATION)
> >   drivers/gpu/drm/drm_pagemap.c:#if IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION)
> > 
> > This results in an objtool warning (or error with CONFIG_OBJTOOL_WERROR)
> > when building with clang because NR_PAGES(order) results in 1U << -1,
> > which causes clang to stop generating code for
> > drm_pagemap_migrate_to_devmem() when encountering unconditional
> > undefined behavior.
> > 
> >   drivers/gpu/drm/drm_gpusvm_helper.o: error: objtool: drm_pagemap_migrate_to_devmem() falls through to next function drm_pagemap_zdd_alloc()
> > 
> > Mark, could please apply the following diff to the -mm merge to avoid
> > this? Obviously, there will need to be further coordination for
> > resolving this upstream when the time comes but it is only an issue in
> > -next currently.
> > 
> > diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
> > index 4a794544b7dc..f00c27edbfb9 100644
> > --- a/drivers/gpu/drm/drm_pagemap.c
> > +++ b/drivers/gpu/drm/drm_pagemap.c
> > @@ -12,7 +12,7 @@
> >  #include <drm/drm_pagemap_util.h>
> >  #include <drm/drm_print.h>
> >  
> > -#if IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION)
> > +#if IS_ENABLED(CONFIG_ARCH_HAS_PMD_SOFTLEAVES)
> >  #define DRM_PAGEMAP_PMD_ORDER	HPAGE_PMD_ORDER
> >  #else
> >  #define DRM_PAGEMAP_PMD_ORDER	(-1)
> > -- 
> > Cheers,
> > Nathan

-- 
Cheers,
Nathan