Re: [PATCH v3 4/9] mm: convert PTE table entries in ptep_get()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] mm: build failure in ptep_get_lockless() with ARCH_HAS_HW_PTE_T
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commit 5a58c0b37be320a1ff8bd51ae9ca94d50bf27375
Author: Muhammad Usama Anjum <usama.anjum@arm.com>

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 software PTE 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_types.h b/include/linux/pgtable_types.h
> index 07da05d375c2c..d6c5a7548550b 100644
> --- a/include/linux/pgtable_types.h
> +++ b/include/linux/pgtable_types.h
> @@ -8,8 +8,10 @@
>  
>  #ifdef CONFIG_ARCH_HAS_HW_PTE_T
>  typedef struct __hw_pte_t { pte_t __pte; } hw_pte_t;
> +#define __pte_from_hw(pte)	((pte).__pte)

[Severity: Low]
Does this wrapper struct cause a build failure in ptep_get_lockless()
when architectures using CONFIG_GUP_GET_PXX_LOW_HIGH (like x86-32 PAE) 
opt into ARCH_HAS_HW_PTE_T?

When hw_pte_t is a wrapper struct instead of a typedef, the direct member 
access fails to compile:

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));
    ...
}

Since ptep is a pointer to the wrapper struct, it lacks the pte_low and
pte_high members.

>  #else
>  #define hw_pte_t pte_t
> +#define __pte_from_hw(pte)	(pte)
>  #endif
>  
>  #endif /* !__ASSEMBLY__ */

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Sashiko AI review · https://sashiko.dev/#/patchset/20260922-pte0-v3-0-5670b8cb9059@arm.com?part=4