Re: [PATCH V3 1/4] arm64/mm: Use pmdp_get() for PMD accesses

[Anshuman Khandual]

On Mon, Oct 05, 2026 at 04:31:28PM +0100, Catalin Marinas wrote:
> On Thu, Sep 24, 2026 at 11:52:11AM +0530, Anshuman Khandual wrote:
> > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> > index 763c5a411d64..9ad2d03e86ad 100644
> > --- a/arch/arm64/include/asm/pgtable.h
> > +++ b/arch/arm64/include/asm/pgtable.h
> > @@ -84,6 +84,12 @@ static inline void arch_leave_lazy_mmu_mode(void)
> >  	arch_flush_lazy_mmu_mode();
> >  }
> >  
> > +#define pmdp_get pmdp_get
> > +static inline pmd_t pmdp_get(pmd_t *pmdp)
> > +{
> > +	return READ_ONCE(*pmdp);
> > +}
> 
> This is the same as the generic version. Does it need redefining?

Without this pmdp_get() override, replacing READ_ONCE() in pmdp_test_and_clear_young()
with pmdp_get() causes a build failure as pmpd_get() which is defined in the generic
pgtable header is not visible from inside platform specific pgtable header, even with
a forward declaration.

Earlier had moved pmdp_test_and_clear_young() inside arch/arm64/mm/mmu.c to avoid the
above described dependency problem. But then realised that pmdp_get() gets eventually
overridden on arm64 platform for D128, why not just redefine here it now as standard
READ_ONCE() to avoid the current build problem and the code movement.

Please find some context here from earlier discussions during V2.

https://lore.kernel.org/all/212067fe-1b16-4b87-87a7-4ce50847eb24@xxxxxxx/

> 
> > +
> >  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> >  #define __HAVE_ARCH_FLUSH_PMD_TLB_RANGE
> >  
> > @@ -811,7 +817,8 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd)
> >  }
> >  
> >  /* Find an entry in the third-level page table. */
> > -#define pte_offset_phys(dir,addr)	(pmd_page_paddr(READ_ONCE(*(dir))) + pte_index(addr) * sizeof(pte_t))
> > +#define pte_offset_phys(dir, addr)	(pmd_page_paddr(pmdp_get(dir)) + \
> > +					 pte_index(addr) * sizeof(pte_t))
> 
> Why not make this change in the generic version?

Could you please elaborate on this ? pte_offset_phys() is arm64 specific helper which
is also local to this header file. AFAICT there is no generic version for this helper.

> 
> -- 
> Catalin