Re: [RESEND v7 02/29] arm64: mm: add PMD swap-exclusive helpers

[David Hildenbrand (Arm)]

On 9/22/26 14:34, Usama Arif wrote:
> 
> 
> On 18/09/2026 22:11, David Hildenbrand (Arm) wrote:
>> On 9/14/26 14:27, Usama Arif wrote:
>>> A later patch keeps a PMD-mapped anonymous THP mapped by a PMD across the
>>> swap round-trip, so PG_anon_exclusive now has to survive in a swap PMD and
>>> not just in a swap PTE.
>>>
>>> arm64 encodes a swap PMD exactly like a swap PTE, so the new helpers wrap
>>> the PTE ones and reuse PTE_SWP_EXCLUSIVE.
>>>
>>> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
>>> Cc: Will Deacon <will@xxxxxxxxxx>
>>> Signed-off-by: Usama Arif <usama.arif@xxxxxxxxx>
>>> ---
>>>  arch/arm64/include/asm/pgtable.h | 6 ++++++
>>>  1 file changed, 6 insertions(+)
>>>
>>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
>>> index e89ec5f4787b4..d3f53a601aed3 100644
>>> --- a/arch/arm64/include/asm/pgtable.h
>>> +++ b/arch/arm64/include/asm/pgtable.h
>>> @@ -599,6 +599,12 @@ static inline int pmd_protnone(pmd_t pmd)
>>>  #define pmd_swp_clear_uffd(pmd) \
>>>  				pte_pmd(pte_swp_clear_uffd(pmd_pte(pmd)))
>>>  #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */
>>> +#ifdef CONFIG_ARCH_HAS_PMD_SOFTLEAVES
>>> +#define pmd_swp_exclusive(pmd)	pte_swp_exclusive(pmd_pte(pmd))
>>> +#define pmd_swp_mkexclusive(pmd)	pte_pmd(pte_swp_mkexclusive(pmd_pte(pmd)))
>>> +#define pmd_swp_clear_exclusive(pmd) \
>>> +				pte_pmd(pte_swp_clear_exclusive(pmd_pte(pmd)))
>>> +#endif
>>
>> Why do we #ifdef that here, but not the uffd-wp swp PMD helper?
>>
> 
> uffd-wp is gated on CONFIG_HAVE_ARCH_USERFAULTFD_WP.
> 
> If I removed the CONFIG_ARCH_HAS_PMD_SOFTLEAVES guards above, when THP=n, arm64
> will use the generic macro which is wrong.
> 
> I tried building uffd-wp swp with just ARCH_HAS_PMD_SOFTLEAVES guard and I got
> the build error 
> 
>   mm/page_table_check.c:232:20: error: implicit declaration of
>   function 'pmd_swp_uffd'
> 
> we will probably need a separate patch like:
> 
>   #ifdef CONFIG_ARCH_HAS_PMD_SOFTLEAVES
>   static inline bool pmd_softleaf_uffd(pmd_t pmd)
>   {
>           return pmd_swp_uffd(pmd);
>   }
>   #else
>   static inline bool pmd_softleaf_uffd(pmd_t pmd)
>   {
>           return false;
>   }
>   #endif
> 
> 
> to avoid the above build error.

Just to explain where I am coming from: for all these patches I took a look how
the other pmd_swp_* functions where handled (and separated from the pte_swp_*
variants). Nothing earth shattering, was mostly looking for keeping things
consistent within these architecture codes.

-- 
Cheers,

David