Re: [PATCH v10 01/10] arm64/mm: add pte_set_huge() and pte_clear_huge()

On Wed, 14 Oct 2026 at 14:03, Dev Jain [off-list ref] wrote:

On 02/10/26 2:39 pm, Wen Jiang wrote:

quoted

vmap installs PTE-level block mappings (PTE_CONT on arm64) by reusing
set_huge_pte_at() and huge_ptep_get_and_clear(), which are HugeTLB
helpers gated by CONFIG_HUGETLB_PAGE. This makes the feature silently
unavailable on CONFIG_HUGETLB_PAGE=n kernels and couples mm/vmalloc.c to
HugeTLB internals it does not otherwise need.

Add pte_set_huge()/pte_clear_huge() to arm64, joining the existing
pmd_set_huge()/pud_set_huge() family in mm/mmu.c. They build on
__set_ptes() and __get_and_clear_full_ptes() directly, so they do not
depend on CONFIG_HUGETLB_PAGE.

There is no caller yet: mm/vmalloc.c is converted later in this series,
once the generic fallbacks are in place.

Signed-off-by: Wen Jiang <redacted>
Reviewed-by: Barry Song <baohua@kernel.org>
---
 arch/arm64/include/asm/pgtable.h |  6 ++++++
 arch/arm64/mm/mmu.c              | 23 +++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 6000905a2e865..9b762eb68cff0 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h

@@ -1978,6 +1978,12 @@ static inline void clear_young_dirty_ptes(struct vm_area_struct *vma,

 #endif /* CONFIG_ARM64_CONTPTE */

+#define __HAVE_ARCH_PTE_SET_HUGE
+void pte_set_huge(pte_t *ptep, unsigned long addr, phys_addr_t phys,
+               pgprot_t prot, unsigned long size);
+#define __HAVE_ARCH_PTE_CLEAR_HUGE
+pte_t pte_clear_huge(pte_t *ptep, unsigned long addr, unsigned long size);
+
 #endif /* !__ASSEMBLER__ */

 #endif /* __ASM_PGTABLE_H */

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 79d90226fd5dc..ae2f15618c97d 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c

@@ -1912,6 +1912,29 @@ int pmd_clear_huge(pmd_t *pmdp)
      return 1;
 }

+void pte_set_huge(pte_t *ptep, unsigned long addr, phys_addr_t phys,
+               pgprot_t prot, unsigned long size)
+{
+     unsigned long pfn = __phys_to_pfn(phys);
+     pte_t pte = pte_mkcont(pfn_pte(pfn, prot));
+     unsigned int nr = size >> PAGE_SHIFT;
+
+     VM_WARN_ON(!IS_ALIGNED(size, CONT_PTE_SIZE));
+     VM_WARN_ON(!IS_ALIGNED(addr, CONT_PTE_SIZE));
+     VM_WARN_ON(!IS_ALIGNED(pfn, CONT_PTES));
+
+     /* For vmap, there is no valid -> valid transition */
+     VM_WARN_ON(pte_valid(__ptep_get(ptep)));
+
+     __set_ptes(&init_mm, addr, ptep, pte, nr);
+}
+
+pte_t pte_clear_huge(pte_t *ptep, unsigned long addr, unsigned long size)
+{
+     return __get_and_clear_full_ptes(&init_mm, addr, ptep,
+                                      size >> PAGE_SHIFT, 0);
+}

I think we should have the same VM_WARN_ON() checks here, as for
pte_clear_huge(), in addition to also warning for
current->mm != &init_mm.

We should make it clear that pte_clear_huge() gets called only for
kernel mappings, and the range we operate on is definitely an aligned
CONT range - which is why we do not go through get_and_clear_full_ptes ->
contpte_get_and_clear_full_ptes, and possibly contpte_try_unfold(), but
directly use __get_and_clear_full_ptes.

Hi Dev,

I'll add the alignment VM_WARN_ON() checks to pte_clear_huge() to
match pte_set_huge().

Regarding the current->mm != &init_mm check: these functions don't take
an mm parameter -- &init_mm is hardcoded in the function body.
current->mm would never equal &init_mm in practice: for user processes it
points to the process's own mm, and for kernel threads it is NULL.
So VM_WARN_ON(current->mm != &init_mm) would always fire.

The existing hugetlb helpers that vmalloc used before this decoupling
(huge_ptep_get_and_clear -> get_clear_contig) also take mm as a
parameter
and don't check current->mm either -- the caller simply passes &init_mm.

How about adding a comment to make the "kernel mapping only" intent
more explicit?
Something like:

 pte_t pte_clear_huge(pte_t *ptep, unsigned long addr, unsigned long size)
 {
+       /* Kernel mappings only */
+
+       VM_WARN_ON(!IS_ALIGNED(size, CONT_PTE_SIZE));
+       VM_WARN_ON(!IS_ALIGNED(addr, CONT_PTE_SIZE));
+
        return __get_and_clear_full_ptes(&init_mm, addr, ptep,
                                         size >> PAGE_SHIFT, 0);
 }

Thanks,
Wen