[PATCH v2 07/13] mm/debug_vm_pgtable/set_pte/pmd/pud: Don't use set_*_at to update an existing pte entry

[Christophe Leroy]

Le 19/08/2020 à 15:01, Aneesh Kumar K.V a écrit :
> set_pte_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_pte_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 at linux.ibm.com>
> ---
>   mm/debug_vm_pgtable.c | 35 +++++++++++++++--------------------
>   1 file changed, 15 insertions(+), 20 deletions(-)
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index 76f4c713e5a3..9c7e2c9cfc76 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -74,15 +74,18 @@ static void __init pte_advanced_tests(struct mm_struct *mm,
>   {
>   	pte_t pte = pfn_pte(pfn, prot);
>   
> +	/*
> +	 * Architectures optimize set_pte_at by avoiding TLB flush.
> +	 * This requires set_pte_at to be not used to update an
> +	 * existing pte entry. Clear pte before we do set_pte_at
> +	 */
> +
>   	pr_debug("Validating PTE advanced\n");
>   	pte = pfn_pte(pfn, prot);
>   	set_pte_at(mm, vaddr, ptep, pte);
>   	ptep_set_wrprotect(mm, vaddr, ptep);
>   	pte = ptep_get(ptep);
>   	WARN_ON(pte_write(pte));
> -
> -	pte = pfn_pte(pfn, prot);
> -	set_pte_at(mm, vaddr, ptep, pte);
>   	ptep_get_and_clear(mm, vaddr, ptep);
>   	pte = ptep_get(ptep);
>   	WARN_ON(!pte_none(pte));
> @@ -96,13 +99,11 @@ static void __init pte_advanced_tests(struct mm_struct *mm,
>   	ptep_set_access_flags(vma, vaddr, ptep, pte, 1);
>   	pte = ptep_get(ptep);
>   	WARN_ON(!(pte_write(pte) && pte_dirty(pte)));
> -
> -	pte = pfn_pte(pfn, prot);
> -	set_pte_at(mm, vaddr, ptep, pte);
>   	ptep_get_and_clear_full(mm, vaddr, ptep, 1);
>   	pte = ptep_get(ptep);
>   	WARN_ON(!pte_none(pte));
>   
> +	pte = pfn_pte(pfn, prot);
>   	pte = pte_mkyoung(pte);
>   	set_pte_at(mm, vaddr, ptep, pte);
>   	ptep_test_and_clear_young(vma, vaddr, ptep);
> @@ -164,9 +165,6 @@ static void __init pmd_advanced_tests(struct mm_struct *mm,
>   	pmdp_set_wrprotect(mm, vaddr, pmdp);
>   	pmd = READ_ONCE(*pmdp);
>   	WARN_ON(pmd_write(pmd));
> -
> -	pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
> -	set_pmd_at(mm, vaddr, pmdp, pmd);
>   	pmdp_huge_get_and_clear(mm, vaddr, pmdp);
>   	pmd = READ_ONCE(*pmdp);
>   	WARN_ON(!pmd_none(pmd));
> @@ -180,13 +178,11 @@ static void __init pmd_advanced_tests(struct mm_struct *mm,
>   	pmdp_set_access_flags(vma, vaddr, pmdp, pmd, 1);
>   	pmd = READ_ONCE(*pmdp);
>   	WARN_ON(!(pmd_write(pmd) && pmd_dirty(pmd)));
> -
> -	pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
> -	set_pmd_at(mm, vaddr, pmdp, pmd);
>   	pmdp_huge_get_and_clear_full(vma, vaddr, pmdp, 1);
>   	pmd = READ_ONCE(*pmdp);
>   	WARN_ON(!pmd_none(pmd));
>   
> +	pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
>   	pmd = pmd_mkyoung(pmd);
>   	set_pmd_at(mm, vaddr, pmdp, pmd);
>   	pmdp_test_and_clear_young(vma, vaddr, pmdp);
> @@ -283,18 +279,10 @@ static void __init pud_advanced_tests(struct mm_struct *mm,
>   	WARN_ON(pud_write(pud));
>   
>   #ifndef __PAGETABLE_PMD_FOLDED

Same as below, once set_put_at() is gone, I don't think this #ifndef 
__PAGETABLE_PMD_FOLDED is still need, should be possible to replace by 
'if (mm_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));
>   
> -	pud = pud_mkhuge(pfn_pud(pfn, prot));
> -	set_pud_at(mm, vaddr, pudp, pud);
> -	pudp_huge_get_and_clear_full(mm, vaddr, pudp, 1);
> -	pud = READ_ONCE(*pudp);
> -	WARN_ON(!pud_none(pud));
>   #endif /* __PAGETABLE_PMD_FOLDED */
>   
>   	pud = pud_mkhuge(pfn_pud(pfn, prot));
> @@ -307,6 +295,13 @@ static void __init pud_advanced_tests(struct mm_struct *mm,
>   	pud = READ_ONCE(*pudp);
>   	WARN_ON(!(pud_write(pud) && pud_dirty(pud)));
>   
> +#ifndef __PAGETABLE_PMD_FOLDED
> +	pudp_huge_get_and_clear_full(vma, vaddr, pudp, 1);
> +	pud = READ_ONCE(*pudp);
> +	WARN_ON(!pud_none(pud));
> +#endif /* __PAGETABLE_PMD_FOLDED */

pudp_huge_get_and_clear_full() and pud_none() are always defined, I 
think this #ifndef can be replaced by an 'if (mm_pmd_folded())'

> +
> +	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);
> 

Christophe