Re: [PATCH] arm64: mm: Drop duplicate check in pmd_trans_huge()

[Gavin Shan]

On 5/8/25 3:44 PM, Anshuman Khandual wrote:
> On 5/8/25 09:21, Gavin Shan wrote:
> > pmd_val(pmd) is inclusive to pmd_present(pmd) since the PMD entry
> > value isn't zero when pmd_present() returns true. Just drop the
> > duplicate check done by pmd_val(pmd).
>
> Agreed, pmd_val() is redundant here because a positive pmd_present()
> also ensures a positive pmd_val().
>
> #define pmd_present(pmd) pte_present(pmd_pte(pmd))
> #define pte_present(pte) (pte_valid(pte) || pte_present_invalid(pte))
>
> #define pte_valid(pte)           (!!(pte_val(pte) & PTE_VALID))
> #define pte_present_invalid(pte) ((pte_val(pte) & (PTE_VALID |
> 				  PTE_PRESENT_INVALID)) == PTE_PRESENT_INVALID)
>
> pte_present() cannot return positive here unless either of the flags
> PTE_VALID or PTE_PRESENT_INVALID is set which implies pte_val() would
> also return positive.
>
> Probably it would be better to add the above details in the commit
> message here as well.

Thanks, I've squashed those details to v2, which was just posted.

> The earlier commit skipped dropping pmd_val() in order to keep then
> proposed change confined to just adding new pmd_table() check, even
> though pmd_val() redundancy was evident as well which should have
> been dropped there after.
>
> d1770e909898 ("arm64/mm: Check pmd_table() in pmd_trans_huge()")

Yes, agreed.

> > No functional changes intended.
> >
> > Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
> > ---
> > Found this by code inspection
> > ---
> >   arch/arm64/include/asm/pgtable.h | 3 +--
> >   1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> > index d3b538be1500..2599b9b8666f 100644
> > --- a/arch/arm64/include/asm/pgtable.h
> > +++ b/arch/arm64/include/asm/pgtable.h
> > @@ -739,8 +739,7 @@ static inline int pmd_trans_huge(pmd_t pmd)
> >   	 * If pmd is present-invalid, pmd_table() won't detect it
> >   	 * as a table, so force the valid bit for the comparison.
> >   	 */
> > -	return pmd_val(pmd) && pmd_present(pmd) &&
> > -	       !pmd_table(__pmd(pmd_val(pmd) | PTE_VALID));
> > +	return pmd_present(pmd) && !pmd_table(__pmd(pmd_val(pmd) | PTE_VALID));
> >   }
> >   #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>

Thanks,
Gavin