Re: [PATCH v10 03/10] mm/vmalloc: use pte_set_huge()/pte_clear_huge() for PTE-level block mappings

[Dev Jain]

On 11/10/26 7:59 pm, Uladzislau Rezki wrote:
> On Fri, Oct 02, 2026 at 05:09:40PM +0800, Wen Jiang wrote:
>> vmap installs PTE-level block mappings by reusing set_huge_pte_at() and
>> huge_ptep_get_and_clear() under #ifdef 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.
>>
>> Now that arm64 and powerpc/8xx provide pte_set_huge() and
>> pte_clear_huge(), add the generic fallbacks next to the existing
>> pmd/pud_set_huge() family and convert vmap_pte_range() and
>> vunmap_pte_range() to the new helpers. The CONFIG_HUGETLB_PAGE guards
>> around the block-mapping paths are dropped, so PTE-level block mappings
>> now also work on CONFIG_HUGETLB_PAGE=n kernels, and mm/vmalloc.c no
>> longer includes <linux/hugetlb.h>.
>>
>> The fallbacks exist only to keep the build working on architectures
>> without PTE-level block mapping support. They are unreachable there:
>> the callers only run when arch_vmap_pte_range_map_size() or
>> arch_vmap_pte_range_unmap_size() return a size other than PAGE_SIZE,
>> which requires an arch implementation. BUILD_BUG() makes that
>> explicit rather than silently doing nothing.
>>
>> Signed-off-by: Wen Jiang <jiangwen6@xxxxxxxxxx>
>> Reviewed-by: Barry Song <baohua@xxxxxxxxxx>
>> ---
>>  include/linux/pgtable.h | 29 +++++++++++++++++++++++++++++
>>  mm/vmalloc.c            | 19 ++++++-------------
>>  2 files changed, 35 insertions(+), 13 deletions(-)
>>
>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>> index 8c093c119e5a8..a7fd51fec8a17 100644
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -2204,6 +2204,35 @@ static inline int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
>>  }
>>  #endif	/* CONFIG_HAVE_ARCH_HUGE_VMAP */
>>  
>> +/*
>> + * PTE-level block mappings for vmap.
>> + *
>> + * pte_set_huge() only has to be implemented by architectures whose
>> + * arch_vmap_pte_range_map_size() can return a size other than PAGE_SIZE.
>> + */
>> +#ifndef __HAVE_ARCH_PTE_SET_HUGE
>> +static inline void pte_set_huge(pte_t *ptep, unsigned long addr,
>> +				phys_addr_t phys, pgprot_t prot,
>> +				unsigned long size)
>> +{
>> +	BUILD_BUG();
>> +}
>> +#endif
>> +
>> +/*
>> + * Likewise, pte_clear_huge() only has to be implemented by architectures
>> + * whose arch_vmap_pte_range_unmap_size() can return a size other than
>> + * PAGE_SIZE.
>> + */
>> +#ifndef __HAVE_ARCH_PTE_CLEAR_HUGE
>> +static inline pte_t pte_clear_huge(pte_t *ptep, unsigned long addr,
>> +				   unsigned long size)
>> +{
>> +	BUILD_BUG();
>> +	return __pte(0);
>> +}
>> +#endif
>> +
>>  #ifndef __HAVE_ARCH_FLUSH_PMD_TLB_RANGE
>>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>  /*
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index bea9f76ed7e74..fb757d95bde25 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -38,7 +38,6 @@
>>  #include <linux/rbtree_augmented.h>
>>  #include <linux/overflow.h>
>>  #include <linux/pgtable.h>
>> -#include <linux/hugetlb.h>
>>  #include <linux/sched/mm.h>
>>  #include <asm/tlbflush.h>
>>  #include <asm/shmparam.h>
>> @@ -100,7 +99,7 @@ static int vmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
>>  	pte_t *pte;
>>  	u64 pfn;
>>  	struct page *page;
>> -	unsigned long size = PAGE_SIZE;
>> +	unsigned long size;
>>  
>>  	if (WARN_ON_ONCE(!PAGE_ALIGNED(end - addr)))
>>  		return -EINVAL;
>> @@ -121,17 +120,12 @@ static int vmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
>>  			BUG();
>>  		}
>>  
>> -#ifdef CONFIG_HUGETLB_PAGE
>>  		size = arch_vmap_pte_range_map_size(addr, end, pfn, max_page_shift);
>>  		if (size != PAGE_SIZE) {
>> -			pte_t entry = pfn_pte(pfn, prot);
>> -
>> -			entry = arch_make_huge_pte(entry, ilog2(size), 0);
>> -			set_huge_pte_at(&init_mm, addr, pte, entry, size);
>> +			pte_set_huge(pte, addr, PFN_PHYS(pfn), prot, size);
>>
> As far as i understand, X86_64 arches do not use this path. This
> specifically is only for ARM64 or powerpc. pte_set_huge() makes me
> thinking about huge-page mappings(PMD/PUD/hugetlb). This helper is

I disagree. All the helpers in hugetlb.c are all "huge" helpers but
the arch overrides.

It has been a long time since huge mappings have been supported at the PTE
level, setting it by setting multiple ptes is just an implementation detail.

Similarly, there are CONT-PMD mappings on arm64, we still call them huge mappings,
it is a matter of implementation that the huge mapping is expressed by setting
multiple PMDs.

 > about mutli page mapping on the PTE level.
> 
> Better naming? pte_set_large()?
> 
> Any thoughts?
> 
> Other then that:
> 
> Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
> 
> --
> Uladzislau Rezki