Re: [PATCH 5/9] mm: convert PTE table entries in ptep_get()

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] ptep_get_lockless() fails to compile when both CONFIG_ARCH_HAS_HW_PTE_T and CONFIG_GUP_GET_PXX_LOW_HIGH are enabled.
--

--- Patch [5]: [PATCH 5/9] mm: convert PTE table entries in ptep_get() ---
commit 697ecf53dc0bc83c57005a208e0294657ed963f8
Author: Muhammad Usama Anjum <[email protected]>

mm: convert PTE table entries in ptep_get()

ptep_get() now accepts a pointer to hw_pte_t storage but must continue to
return a logical pte_t value. Add __pte_from_hw for both generic hw_pte_t
definitions. Read the hw_pte_t table element atomically before converting
it to pte_t.

> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index dad80d264aac2..1768421755a9c 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -493,7 +493,7 @@ static inline int pudp_set_access_flags(struct vm_area_struct *vma,
>  #ifndef ptep_get
>  static inline pte_t ptep_get(hw_pte_t *ptep)
>  {
> -	return READ_ONCE(*ptep);
> +	return __pte_from_hw(READ_ONCE(*ptep));
>  }
>  #endif

[Severity: Low]
Does this change cause a compilation failure in ptep_get_lockless() when
CONFIG_GUP_GET_PXX_LOW_HIGH and CONFIG_ARCH_HAS_HW_PTE_T are both enabled?

When CONFIG_ARCH_HAS_HW_PTE_T is enabled, hw_pte_t becomes a wrapper struct.
However, ptep_get_lockless() still attempts to access pte_low and pte_high
directly from the hw_pte_t pointer:

include/linux/pgtable.h:ptep_get_lockless() {
        ...
	do {
		pte.pte_low = ptep->pte_low;
		smp_rmb();
		pte.pte_high = ptep->pte_high;
		smp_rmb();
	} while (unlikely(pte.pte_low != ptep->pte_low));
        ...
}

Should ptep_get_lockless() be updated to handle the wrapper struct, perhaps
by accessing the __pte member or extracting the logical pte_t first?

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=5