[PATCH v2 0/5] mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and vmemmap_check_pmd()

[PATCH v2 0/5] mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and vmemmap_check_pmd()

[Muchun Song]

The two weak functions vmemmap_set_pmd() and vmemmap_check_pmd() are
currently no-ops on every architecture, forcing each platform that needs
them to duplicate the same handful of lines. Provide a generic implementation:

- vmemmap_set_pmd() simply sets a huge PMD with PAGE_KERNEL protection.

- vmemmap_check_pmd() verifies that the PMD is present and leaf,
  then calls the existing vmemmap_verify() helper.

Architectures that need special handling can continue to override the
weak symbols; everyone else gets the standard version for free.

This series drops the custom implementations in arm64, riscv, loongarch,
and sparc, replacing them with the generic implementation introduced
in the first patch.

v1 -> v2:
- Fixed a tooling issue in v1 where duplicate/conflicting patches
  were incorrectly sent to the mailing list. No code changes compared
  to the intended v1.


Muchun Song (5):
  mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and
    vmemmap_check_pmd()
  arm64/mm: drop vmemmap_pmd helpers and use generic code
  riscv/mm: drop vmemmap_pmd helpers and use generic code
  loongarch/mm: drop vmemmap_check_pmd helper and use generic code
  sparc/mm: drop vmemmap_check_pmd helper and use generic code

 arch/arm64/mm/mmu.c      | 14 --------------
 arch/loongarch/mm/init.c | 11 -----------
 arch/riscv/mm/init.c     | 13 -------------
 arch/sparc/mm/init_64.c  | 11 -----------
 mm/sparse-vmemmap.c      |  7 ++++++-
 5 files changed, 6 insertions(+), 50 deletions(-)

-- 
2.20.1

[PATCH v2 2/5] arm64/mm: drop vmemmap_pmd helpers and use generic code

[Muchun Song]

The generic implementations now suffice; remove the arm64 copies.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 arch/arm64/mm/mmu.c | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index ec1c6971a561..b87053452641 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1745,20 +1745,6 @@ static void free_empty_tables(unsigned long addr, unsigned long end,
 }
 #endif
 
-void __meminit vmemmap_set_pmd(pmd_t *pmdp, void *p, int node,
-			       unsigned long addr, unsigned long next)
-{
-	pmd_set_huge(pmdp, __pa(p), __pgprot(PROT_SECT_NORMAL));
-}
-
-int __meminit vmemmap_check_pmd(pmd_t *pmdp, int node,
-				unsigned long addr, unsigned long next)
-{
-	vmemmap_verify((pte_t *)pmdp, node, addr, next);
-
-	return pmd_sect(READ_ONCE(*pmdp));
-}
-
 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 		struct vmem_altmap *altmap)
 {
-- 
2.20.1

Re: [PATCH v2 2/5] arm64/mm: drop vmemmap_pmd helpers and use generic code

[Will Deacon]

On Sat, Apr 04, 2026 at 08:20:55PM +0800, Muchun Song wrote:
> The generic implementations now suffice; remove the arm64 copies.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  arch/arm64/mm/mmu.c | 14 --------------
>  1 file changed, 14 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index ec1c6971a561..b87053452641 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1745,20 +1745,6 @@ static void free_empty_tables(unsigned long addr, unsigned long end,
>  }
>  #endif
>  
> -void __meminit vmemmap_set_pmd(pmd_t *pmdp, void *p, int node,
> -			       unsigned long addr, unsigned long next)
> -{
> -	pmd_set_huge(pmdp, __pa(p), __pgprot(PROT_SECT_NORMAL));
> -}
> -
> -int __meminit vmemmap_check_pmd(pmd_t *pmdp, int node,
> -				unsigned long addr, unsigned long next)
> -{
> -	vmemmap_verify((pte_t *)pmdp, node, addr, next);
> -
> -	return pmd_sect(READ_ONCE(*pmdp));
> -}

I think this is fine:

Acked-by: Will Deacon <will@kernel.org>

but note that, since c25c4aa3f79a ("arm64: mm: Add PTE_DIRTY back to
PAGE_KERNEL* to fix kexec/hibernation"), I think that using PAGE_KERNEL
(like the generic code does in the first patch of this series) means
that this change isn't a no-op -- it means that the huge entries will
now be marked as dirty. That's possibly a bug fix (?)

Will

Re: [PATCH v2 2/5] arm64/mm: drop vmemmap_pmd helpers and use generic code

[Muchun Song]

> On May 18, 2026, at 20:33, Will Deacon <will@kernel.org> wrote:
> 
> On Sat, Apr 04, 2026 at 08:20:55PM +0800, Muchun Song wrote:
>> The generic implementations now suffice; remove the arm64 copies.
>> 
>> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>> ---
>> arch/arm64/mm/mmu.c | 14 --------------
>> 1 file changed, 14 deletions(-)
>> 
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index ec1c6971a561..b87053452641 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -1745,20 +1745,6 @@ static void free_empty_tables(unsigned long addr, unsigned long end,
>> }
>> #endif
>> 
>> -void __meminit vmemmap_set_pmd(pmd_t *pmdp, void *p, int node,
>> -       unsigned long addr, unsigned long next)
>> -{
>> - 	pmd_set_huge(pmdp, __pa(p), __pgprot(PROT_SECT_NORMAL));
>> -}
>> -
>> -int __meminit vmemmap_check_pmd(pmd_t *pmdp, int node,
>> - unsigned long addr, unsigned long next)
>> -{
>> - 	vmemmap_verify((pte_t *)pmdp, node, addr, next);
>> -
>> - 	return pmd_sect(READ_ONCE(*pmdp));
>> -}
> 
> I think this is fine:
> 
> Acked-by: Will Deacon <will@kernel.org>

Thanks.

> 
> but note that, since c25c4aa3f79a ("arm64: mm: Add PTE_DIRTY back to
> PAGE_KERNEL* to fix kexec/hibernation"), I think that using PAGE_KERNEL
> (like the generic code does in the first patch of this series) means
> that this change isn't a no-op -- it means that the huge entries will
> now be marked as dirty. That's possibly a bug fix (?)

I think you are right. We should mark kernel mapping as dirty.

Thanks,
Muchun

> 
> Will

Re: [PATCH v2 0/5] mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and vmemmap_check_pmd()

[patchwork-bot+linux-riscv]

Hello:

This patch was applied to riscv/linux.git (fixes)
by Andrew Morton <akpm@linux-foundation.org>:

On Sat,  4 Apr 2026 20:20:53 +0800 you wrote:
> The two weak functions vmemmap_set_pmd() and vmemmap_check_pmd() are
> currently no-ops on every architecture, forcing each platform that needs
> them to duplicate the same handful of lines. Provide a generic implementation:
> 
> - vmemmap_set_pmd() simply sets a huge PMD with PAGE_KERNEL protection.
> 
> - vmemmap_check_pmd() verifies that the PMD is present and leaf,
>   then calls the existing vmemmap_verify() helper.
> 
> [...]

Here is the summary with links:
  - [v2,3/5] riscv/mm: drop vmemmap_pmd helpers and use generic code
    https://git.kernel.org/riscv/c/abff0ecf7602

You are awesome, thank you!
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