[PATCH v3 0/5] mm/sparse-vmemmap: Provide generic vmemmap_set_pmd() and vmemmap_check_pmd()

[PATCH v3 0/5] mm/sparse-vmemmap: Provide generic vmemmap_set_pmd() and vmemmap_check_pmd()

[Muchun Song]

The weak vmemmap_set_pmd() and vmemmap_check_pmd() hooks are
currently no-ops in the generic code, which leaves architectures that
need PMD-level handling to open-code the same logic locally.

This series provides generic implementations for both helpers in
mm/sparse-vmemmap.c. vmemmap_set_pmd() installs a huge PMD with
PAGE_KERNEL protection, and vmemmap_check_pmd() verifies a present
leaf PMD before reusing the existing vmemmap_verify() helper.

With those generic helpers in place, patches 2-5 remove the now
redundant arch-specific implementations from arm64, riscv, loongarch,
and sparc.

v2 -> v3:
- Replace BUG_ON() with WARN_ON_ONCE() in patch 1
- Add Will Deacon's Acked-by to patch 2

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(-)


base-commit: 7da7f07112610a520567421dd2ffcb51beaefbcc
-- 
2.54.0

[PATCH v3 1/5] mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and vmemmap_check_pmd()

[Muchun Song]

The two weak functions 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.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
v2->v3:
- Replace BUG_ON() with WARN_ON_ONCE() in vmemmap_set_pmd()
---
 mm/sparse-vmemmap.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 112ccf9c71ca..99e2be39671b 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -386,12 +386,17 @@ int __meminit vmemmap_populate_hvo(unsigned long addr, unsigned long end,
 void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
 				      unsigned long addr, unsigned long next)
 {
+	WARN_ON_ONCE(!pmd_set_huge(pmd, virt_to_phys(p), PAGE_KERNEL));
 }
 
 int __weak __meminit vmemmap_check_pmd(pmd_t *pmd, int node,
 				       unsigned long addr, unsigned long next)
 {
-	return 0;
+	if (!pmd_leaf(pmdp_get(pmd)))
+		return 0;
+	vmemmap_verify((pte_t *)pmd, node, addr, next);
+
+	return 1;
 }
 
 int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end,
-- 
2.54.0

Re: [PATCH v3 1/5] mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and vmemmap_check_pmd()

[David Hildenbrand (Arm)]

On 6/1/26 10:48, Muchun Song wrote:
> The two weak functions 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.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
> v2->v3:
> - Replace BUG_ON() with WARN_ON_ONCE() in vmemmap_set_pmd()
> ---
>  mm/sparse-vmemmap.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index 112ccf9c71ca..99e2be39671b 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -386,12 +386,17 @@ int __meminit vmemmap_populate_hvo(unsigned long addr, unsigned long end,
>  void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
>  				      unsigned long addr, unsigned long next)
>  {
> +	WARN_ON_ONCE(!pmd_set_huge(pmd, virt_to_phys(p), PAGE_KERNEL));


Not sure if a VM_WARN_ON_ONCE() would be appropriate. (then, we have to move the
pmd_set_huge() out of the statement).

Acked-by: David Hildenbrand (Arm) <david@kernel.org>


-- 
Cheers,

David

Re: [PATCH v3 1/5] mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and vmemmap_check_pmd()

[Muchun Song]

> On Jun 1, 2026, at 20:22, David Hildenbrand (Arm) <david@kernel.org> wrote:
> 
> On 6/1/26 10:48, Muchun Song wrote:
>> The two weak functions 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.
>> 
>> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>> ---
>> v2->v3:
>> - Replace BUG_ON() with WARN_ON_ONCE() in vmemmap_set_pmd()
>> ---
>> mm/sparse-vmemmap.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>> 
>> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
>> index 112ccf9c71ca..99e2be39671b 100644
>> --- a/mm/sparse-vmemmap.c
>> +++ b/mm/sparse-vmemmap.c
>> @@ -386,12 +386,17 @@ int __meminit vmemmap_populate_hvo(unsigned long addr, unsigned long end,
>> void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
>>       unsigned long addr, unsigned long next)
>> {
>> + 	WARN_ON_ONCE(!pmd_set_huge(pmd, virt_to_phys(p), PAGE_KERNEL));
> 
> 
> Not sure if a VM_WARN_ON_ONCE() would be appropriate. (then, we have to move the
> pmd_set_huge() out of the statement).

I think it might be better to keep WARN_ON_ONCE here. This way, we can still
monitor for warnings in production while keeping the code simple.

> 
> Acked-by: David Hildenbrand (Arm) <david@kernel.org>

Thanks.

> 
> 
> -- 
> Cheers,
> 
> David

Re: [PATCH v3 1/5] mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and vmemmap_check_pmd()

[Oscar Salvador (SUSE)]

On Mon, Jun 01, 2026 at 08:37:42PM +0800, Muchun Song wrote:
> 
> 
> > On Jun 1, 2026, at 20:22, David Hildenbrand (Arm) <david@kernel.org> wrote:
> > 
> > On 6/1/26 10:48, Muchun Song wrote:
> >> The two weak functions 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.
> >> 
> >> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> >> ---
> >> v2->v3:
> >> - Replace BUG_ON() with WARN_ON_ONCE() in vmemmap_set_pmd()
> >> ---
> >> mm/sparse-vmemmap.c | 7 ++++++-
> >> 1 file changed, 6 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> >> index 112ccf9c71ca..99e2be39671b 100644
> >> --- a/mm/sparse-vmemmap.c
> >> +++ b/mm/sparse-vmemmap.c
> >> @@ -386,12 +386,17 @@ int __meminit vmemmap_populate_hvo(unsigned long addr, unsigned long end,
> >> void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
> >>       unsigned long addr, unsigned long next)
> >> {
> >> + 	WARN_ON_ONCE(!pmd_set_huge(pmd, virt_to_phys(p), PAGE_KERNEL));
> > 
> > 
> > Not sure if a VM_WARN_ON_ONCE() would be appropriate. (then, we have to move the
> > pmd_set_huge() out of the statement).
> 
> I think it might be better to keep WARN_ON_ONCE here. This way, we can still
> monitor for warnings in production while keeping the code simple.

IIRC there was a discussion about this some time ago, given the fact that quite
some people out there tend to have 'panic_on_warn', but then again, if we fail to
set a PMD here it means something pretty nasty happened, so I am ok with that.

 

-- 
Oscar Salvador
SUSE Labs

Re: [PATCH v3 1/5] mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and vmemmap_check_pmd()

[Oscar Salvador (SUSE)]

On Mon, Jun 01, 2026 at 04:48:40PM +0800, Muchun Song wrote:
> The two weak functions 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.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Acked-by: Oscar Salvador (SUSE) <osalvador@kernel.org>

 

-- 
Oscar Salvador
SUSE Labs

[PATCH v3 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>
Acked-by: Will Deacon <will@kernel.org>
---
v2->v3:
- Collect Acked-by from Will Deacon
---
 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 24388e5c727d..ea10b0ebecd7 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1776,20 +1776,6 @@ 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_leaf(READ_ONCE(*pmdp));
-}
-
 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 		struct vmem_altmap *altmap)
 {
-- 
2.54.0

Re: [PATCH v3 2/5] arm64/mm: drop vmemmap_pmd helpers and use generic code

[David Hildenbrand (Arm)]

On 6/1/26 10:48, Muchun Song wrote:
> The generic implementations now suffice; remove the arm64 copies.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Acked-by: Will Deacon <will@kernel.org>
> ---

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH v3 2/5] arm64/mm: drop vmemmap_pmd helpers and use generic code

[Oscar Salvador (SUSE)]

On Mon, Jun 01, 2026 at 04:48:41PM +0800, Muchun Song wrote:
> The generic implementations now suffice; remove the arm64 copies.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Acked-by: Will Deacon <will@kernel.org>

Reviewed-by: Oscar Salvador (SUSE) <osalvador@kernel.org>

> ---
> v2->v3:
> - Collect Acked-by from Will Deacon
> ---
>  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 24388e5c727d..ea10b0ebecd7 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1776,20 +1776,6 @@ 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_leaf(READ_ONCE(*pmdp));
> -}
> -
>  int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
>  		struct vmem_altmap *altmap)
>  {
> -- 
> 2.54.0
> 
> 

-- 
Oscar Salvador
SUSE Labs

[PATCH v3 3/5] riscv/mm: drop vmemmap_pmd helpers and use generic code

[Muchun Song]

The generic implementations now suffice; remove the riscv copies.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 arch/riscv/mm/init.c | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 885f1db4e9bf..5f680eb83e86 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -1359,19 +1359,6 @@ void __init misc_mem_init(void)
 }
 
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
-void __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
-			       unsigned long addr, unsigned long next)
-{
-	pmd_set_huge(pmd, virt_to_phys(p), PAGE_KERNEL);
-}
-
-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 1;
-}
-
 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 			       struct vmem_altmap *altmap)
 {
-- 
2.54.0

Re: [PATCH v3 3/5] riscv/mm: drop vmemmap_pmd helpers and use generic code

[David Hildenbrand (Arm)]

On 6/1/26 10:48, Muchun Song wrote:
> The generic implementations now suffice; remove the riscv copies.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH v3 3/5] riscv/mm: drop vmemmap_pmd helpers and use generic code

[Oscar Salvador (SUSE)]

On Mon, Jun 01, 2026 at 04:48:42PM +0800, Muchun Song wrote:
> The generic implementations now suffice; remove the riscv copies.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Reviewed-by: Oscar Salvador (SUSE) <osalvador@kernel.org>

 

-- 
Oscar Salvador
SUSE Labs

[PATCH v3 4/5] loongarch/mm: drop vmemmap_check_pmd helper and use generic code

[Muchun Song]

The generic implementations now suffice; remove the loongarch copies.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 arch/loongarch/mm/init.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/arch/loongarch/mm/init.c b/arch/loongarch/mm/init.c
index 687980b6e91f..3407030f3e7a 100644
--- a/arch/loongarch/mm/init.c
+++ b/arch/loongarch/mm/init.c
@@ -140,17 +140,6 @@ void __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
 	set_pmd_at(&init_mm, addr, pmd, entry);
 }
 
-int __meminit vmemmap_check_pmd(pmd_t *pmd, int node,
-				unsigned long addr, unsigned long next)
-{
-	int huge = pmd_val(pmdp_get(pmd)) & _PAGE_HUGE;
-
-	if (huge)
-		vmemmap_verify((pte_t *)pmd, node, addr, next);
-
-	return huge;
-}
-
 int __meminit vmemmap_populate(unsigned long start, unsigned long end,
 			       int node, struct vmem_altmap *altmap)
 {
-- 
2.54.0

Re: [PATCH v3 4/5] loongarch/mm: drop vmemmap_check_pmd helper and use generic code

[David Hildenbrand (Arm)]

On 6/1/26 10:48, Muchun Song wrote:
> The generic implementations now suffice; remove the loongarch copies.

You are only removing a single function? So "copy"


Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH v3 4/5] loongarch/mm: drop vmemmap_check_pmd helper and use generic code

[Muchun Song]

> On Jun 1, 2026, at 20:24, David Hildenbrand (Arm) <david@kernel.org> wrote:
> 
> On 6/1/26 10:48, Muchun Song wrote:
>> The generic implementations now suffice; remove the loongarch copies.
> 
> You are only removing a single function? So "copy"

Yes. I copied the commit message from other commit and forgot to update
accordingly.

> 
> 
> Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>

Thanks.

> 
> -- 
> Cheers,
> 
> David

Re: [PATCH v3 4/5] loongarch/mm: drop vmemmap_check_pmd helper and use generic code

[Oscar Salvador (SUSE)]

On Mon, Jun 01, 2026 at 04:48:43PM +0800, Muchun Song wrote:
> The generic implementations now suffice; remove the loongarch copies.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Reviewed-by: Oscar Salvador (SUSE) <osalvador@kernel.org>

 

-- 
Oscar Salvador
SUSE Labs

[PATCH v3 5/5] sparc/mm: drop vmemmap_check_pmd helper and use generic code

[Muchun Song]

The generic implementations now suffice; remove the sparc copies.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 arch/sparc/mm/init_64.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
index 3b679b1d1d72..103db4683b16 100644
--- a/arch/sparc/mm/init_64.c
+++ b/arch/sparc/mm/init_64.c
@@ -2559,17 +2559,6 @@ void __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
 	pmd_val(*pmd) = pte_base | __pa(p);
 }
 
-int __meminit vmemmap_check_pmd(pmd_t *pmdp, int node,
-				unsigned long addr, unsigned long next)
-{
-	int large = pmd_leaf(*pmdp);
-
-	if (large)
-		vmemmap_verify((pte_t *)pmdp, node, addr, next);
-
-	return large;
-}
-
 int __meminit vmemmap_populate(unsigned long vstart, unsigned long vend,
 			       int node, struct vmem_altmap *altmap)
 {
-- 
2.54.0

Re: [PATCH v3 5/5] sparc/mm: drop vmemmap_check_pmd helper and use generic code

[David Hildenbrand (Arm)]

On 6/1/26 10:48, Muchun Song wrote:
> The generic implementations now suffice; remove the sparc copies.

"copy"

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH v3 5/5] sparc/mm: drop vmemmap_check_pmd helper and use generic code

[Oscar Salvador (SUSE)]

On Mon, Jun 01, 2026 at 04:48:44PM +0800, Muchun Song wrote:
> The generic implementations now suffice; remove the sparc copies.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Reviewed-by: Oscar Salvador (SUSE) <osalvador@kernel.org>

 

-- 
Oscar Salvador
SUSE Labs