Re: [RFC PATCH 2/3] powerpc/mm: Implement pmdp_establish for ppc64

[Michal Hocko <mhocko@kernel.org>]

On Thu 27-07-17 14:07:55, Aneesh Kumar K.V wrote:
> We can now use this to set pmd page table entries to absolute values. THP
> need to ensure that we always update pmd PTE entries such that we never mark
> the pmd none. pmdp_establish helps in implementing that.
> 
> This doesn't flush the tlb. Based on the old_pmd value returned caller can
> decide to call flush_pmd_tlb_range()

_Why_ do we need this. It doesn't really help that the newly added
function is not used so we could check that...

> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> ---
>  arch/powerpc/include/asm/book3s/64/radix.h |  9 ++++++---
>  arch/powerpc/mm/pgtable-book3s64.c         | 10 ++++++++++
>  2 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/radix.h b/arch/powerpc/include/asm/book3s/64/radix.h
> index cd481ab601b6..558fea3b2d22 100644
> --- a/arch/powerpc/include/asm/book3s/64/radix.h
> +++ b/arch/powerpc/include/asm/book3s/64/radix.h
> @@ -131,7 +131,8 @@ static inline unsigned long __radix_pte_update(pte_t *ptep, unsigned long clr,
>  	do {
>  		pte = READ_ONCE(*ptep);
>  		old_pte = pte_val(pte);
> -		new_pte = (old_pte | set) & ~clr;
> +		new_pte = old_pte & ~clr;
> +		new_pte |= set;
>  
>  	} while (!pte_xchg(ptep, __pte(old_pte), __pte(new_pte)));
>  
> @@ -153,9 +154,11 @@ static inline unsigned long radix__pte_update(struct mm_struct *mm,
>  
>  		old_pte = __radix_pte_update(ptep, ~0ul, 0);
>  		/*
> -		 * new value of pte
> +		 * new value of pte. We clear all the bits in clr mask
> +		 * first and set the bits in set mask.
>  		 */
> -		new_pte = (old_pte | set) & ~clr;
> +		new_pte = old_pte & ~clr;
> +		new_pte |= set;
>  		radix__flush_tlb_pte_p9_dd1(old_pte, mm, addr);
>  		if (new_pte)
>  			__radix_pte_update(ptep, 0, new_pte);
> diff --git a/arch/powerpc/mm/pgtable-book3s64.c b/arch/powerpc/mm/pgtable-book3s64.c
> index 0bb7f824ecdd..7100b0150a2a 100644
> --- a/arch/powerpc/mm/pgtable-book3s64.c
> +++ b/arch/powerpc/mm/pgtable-book3s64.c
> @@ -45,6 +45,16 @@ int pmdp_set_access_flags(struct vm_area_struct *vma, unsigned long address,
>  	return changed;
>  }
>  
> +pmd_t pmdp_establish(struct vm_area_struct *vma, unsigned long addr,
> +		     pmd_t *pmdp, pmd_t entry)
> +{
> +	long pmdval;
> +
> +	pmdval = pmd_hugepage_update(vma->vm_mm, addr, pmdp, ~0UL, pmd_val(entry));
> +	return __pmd(pmdval);
> +}
> +
> +
>  int pmdp_test_and_clear_young(struct vm_area_struct *vma,
>  			      unsigned long address, pmd_t *pmdp)
>  {
> -- 
> 2.13.3
> 
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-- 
Michal Hocko
SUSE Labs

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