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Subject: Re: [PATCH 09/16] debug_vm_pgtable/set_pud: Don't use set_pud_at to
 update an existing pud entry
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>, linux-mm@kvack.org,
 akpm@linux-foundation.org
References: <20200812063358.369514-1-aneesh.kumar@linux.ibm.com>
 <20200812063358.369514-9-aneesh.kumar@linux.ibm.com>
From: Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <6f25f770-3e5d-e823-eb05-1a8a6f5c0f93@arm.com>
Date: Wed, 12 Aug 2020 18:16:43 +0530
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On 08/12/2020 12:03 PM, Aneesh Kumar K.V wrote:
> set_pud_at() should not be used to set a pte entry at locations that
> already holds a valid pte entry. Architectures like ppc64 don't do TLB
> invalidate in set_pud_at() and hence expect it to be used to set locations
> that are not a valid PTE.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>  mm/debug_vm_pgtable.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index 60bf876081b8..644d28861ce9 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -278,9 +278,6 @@ static void __init pud_advanced_tests(struct mm_struct *mm,
>  	WARN_ON(pud_write(pud));
>  
>  #ifndef __PAGETABLE_PMD_FOLDED
> -
> -	pud = pud_mkhuge(pfn_pud(pfn, prot));
> -	set_pud_at(mm, vaddr, pudp, pud);
>  	pudp_huge_get_and_clear(mm, vaddr, pudp);
>  	pud = READ_ONCE(*pudp);
>  	WARN_ON(!pud_none(pud));
> @@ -302,6 +299,11 @@ static void __init pud_advanced_tests(struct mm_struct *mm,
>  	pud = READ_ONCE(*pudp);
>  	WARN_ON(!(pud_write(pud) && pud_dirty(pud)));
>  
> +	pudp_huge_get_and_clear_full(vma, vaddr, pudp, 1);
> +	pud = READ_ONCE(*pudp);
> +	WARN_ON(!pud_none(pud));
> +
> +	pud = pud_mkhuge(pfn_pud(pfn, prot));
>  	pud = pud_mkyoung(pud);
>  	set_pud_at(mm, vaddr, pudp, pud);
>  	pudp_test_and_clear_young(vma, vaddr, pudp);

Very similar to [PATCH 3/16] wrt set_pte_at(), please fold it.