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

[Usama Arif <usama.arif@linux.dev>]

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@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Signed-off-by: Usama Arif <usama.arif@linux.dev>
>> ---
>>  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.