Re: [PATCH 1/6] arm64: use hw_pte_t for HW PTE pointers

[Ryan Roberts <ryan.roberts@arm.com>]

On 14/09/2026 14:51, Muhammad Usama Anjum wrote:
> With pte_t * used for HW PTE pointers, the compiler cannot distinguish
> them from SW PTE value pointers. The generic HW PTE interfaces already
> use hw_pte_t *, so arm64 HW PTE pointers must use that type before
> ARCH_HAS_HW_PTE_T can make it distinct.
> 
> Convert HW PTE pointers to hw_pte_t *, retaining pte_t for SW PTE
> values. Helpers shared with PMD and PUD operations keep explicit casts
> because this series does not introduce distinct entry types for those
> levels.
> 
> arm64 still uses the hw_pte_t alias in this patch. The new pointer
> spelling therefore denotes the same type until the final opt-in.
> 
> Include linux/pgtable_types.h in pi.h to make hw_pte_t visible.
> 
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> ---
>  arch/arm64/include/asm/hugetlb.h  |  19 ++---
>  arch/arm64/include/asm/pgalloc.h  |   2 +-
>  arch/arm64/include/asm/pgtable.h  | 143 ++++++++++++++++++++------------------
>  arch/arm64/include/asm/vmalloc.h  |   2 +-
>  arch/arm64/kernel/efi.c           |   3 +-
>  arch/arm64/kernel/pi/map_kernel.c |   4 +-
>  arch/arm64/kernel/pi/map_range.c  |   9 +--
>  arch/arm64/kernel/pi/pi.h         |   3 +-
>  arch/arm64/mm/contpte.c           |  49 +++++++------
>  arch/arm64/mm/fault.c             |   5 +-
>  arch/arm64/mm/fixmap.c            |   6 +-
>  arch/arm64/mm/hugetlbpage.c       |  48 +++++++------
>  arch/arm64/mm/kasan_init.c        |   4 +-
>  arch/arm64/mm/mmu.c               |  46 +++++++-----
>  arch/arm64/mm/pageattr.c          |   4 +-
>  arch/arm64/mm/trans_pgd.c         |   4 +-
>  16 files changed, 190 insertions(+), 161 deletions(-)
> 

[...]

> diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c
> index f66a0016dd02d..237a9136bc73b 100644
> --- a/arch/arm64/mm/fixmap.c
> +++ b/arch/arm64/mm/fixmap.c
> @@ -35,7 +35,7 @@ static pte_t bm_pte[NR_BM_PTE_TABLES][PTRS_PER_PTE] __bss_pgtbl;
>  static pmd_t bm_pmd[PTRS_PER_PMD] __bss_pgtbl __maybe_unused;
>  static pud_t bm_pud[PTRS_PER_PUD] __bss_pgtbl __maybe_unused;
>  
> -static inline pte_t *fixmap_pte(unsigned long addr)
> +static inline hw_pte_t *fixmap_pte(unsigned long addr)
>  {
>  	return &bm_pte[BM_PTE_TABLE_IDX(addr)][pte_index(addr)];

How does this work, given you haven't yet converted bm_pte? You're returning a
pte_t* where you need a hw_pte_t*. Either the compiler is implicitly converting
(which would defeat the whole purpose of this series) or this patch doesn't
compile until you convert bm_pte later on (which I suspect is more likely).

>  }
> @@ -43,7 +43,7 @@ static inline pte_t *fixmap_pte(unsigned long addr)
>  static void __init early_fixmap_init_pte(pmd_t *pmdp, unsigned long addr)
>  {
>  	pmd_t pmd = READ_ONCE(*pmdp);
> -	pte_t *ptep;
> +	hw_pte_t *ptep;
>  
>  	if (pmd_none(pmd)) {
>  		ptep = bm_pte[BM_PTE_TABLE_IDX(addr)];

Same problem here?

Thanks,
Ryan