Re: [RESEND v7 07/29] x86: mm: add PMD swap-exclusive helpers

[David Hildenbrand (Arm)]

On 9/14/26 14:27, Usama Arif wrote:
> A later patch keeps a PMD-mapped anonymous THP mapped by a PMD across the

As a general note, we try not to talk about "this patch" or "later patches".

Instead, just say "Prepare for X by doing Y.".

> swap round-trip, so PG_anon_exclusive now has to survive in a swap PMD and
> not just in a swap PTE.
> 
> x86-64 encodes a swap PMD exactly like a swap PTE, so the new helpers reuse
> _PAGE_SWP_EXCLUSIVE, bit 3, which the swap-entry layout already reserves
> for PG_anon_exclusive. 32-bit x86 aliases that bit to _PAGE_PSE and does
> not select ARCH_HAS_PMD_SOFTLEAVES.
> 
> Cc: Thomas Gleixner <tglx@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Signed-off-by: Usama Arif <usama.arif@xxxxxxxxx>
> ---
>  arch/x86/include/asm/pgtable.h | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index d551120a7c889..a2d1cd03cba23 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -1525,6 +1525,23 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
>  	return pte_clear_flags(pte, _PAGE_SWP_EXCLUSIVE);
>  }
>  
> +#ifdef CONFIG_ARCH_HAS_PMD_SOFTLEAVES
> +static inline pmd_t pmd_swp_mkexclusive(pmd_t pmd)
> +{
> +	return pmd_set_flags(pmd, _PAGE_SWP_EXCLUSIVE);
> +}
> +
> +static inline bool pmd_swp_exclusive(pmd_t pmd)
> +{
> +	return pmd_flags(pmd) & _PAGE_SWP_EXCLUSIVE;
> +}
> +
> +static inline pmd_t pmd_swp_clear_exclusive(pmd_t pmd)
> +{
> +	return pmd_clear_flags(pmd, _PAGE_SWP_EXCLUSIVE);
> +}
> +#endif
> +
>  #ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
>  static inline pte_t pte_swp_mksoft_dirty(pte_t pte)
>  {

Reviewed-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

-- 
Cheers,

David