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

[Dev Jain <dev.jain@arm.com>]

On 02/10/26 2:39 pm, Wen Jiang wrote:
> 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 <jiangwen6@xiaomi.com>
> 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.


> +
>  int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)
>  {
>  	pte_t *table;