From: Anshuman Khandual <anshuman.khandual@arm.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
linux-mm@kvack.org, akpm@linux-foundation.org
Cc: linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 13/16] debug_vm_pgtable/pmd_clear: Don't use pmd/pud_clear on pte entries
Date: Thu, 13 Aug 2020 10:57:41 +0530 [thread overview]
Message-ID: <1bb841d2-4622-b122-7176-246eb3702c9f@arm.com> (raw)
In-Reply-To: <20200812063358.369514-13-aneesh.kumar@linux.ibm.com>
On 08/12/2020 12:03 PM, Aneesh Kumar K.V wrote:
> pmd_clear() should not be used to clear pmd level pte entries.
Could you please elaborate on this. The proposed change set does
not match the description here.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
> mm/debug_vm_pgtable.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index 061c19bba7f0..529892b9be2f 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -191,6 +191,8 @@ static void __init pmd_advanced_tests(struct mm_struct *mm,
> pmd = READ_ONCE(*pmdp);
> WARN_ON(pmd_young(pmd));
>
> + /* Clear the pte entries */
> + pmdp_huge_get_and_clear(mm, vaddr, pmdp);
> pgtable = pgtable_trans_huge_withdraw(mm, pmdp);
> }
>
> @@ -313,6 +315,8 @@ static void __init pud_advanced_tests(struct mm_struct *mm,
> pudp_test_and_clear_young(vma, vaddr, pudp);
> pud = READ_ONCE(*pudp);
> WARN_ON(pud_young(pud));
> +
> + pudp_huge_get_and_clear(mm, vaddr, pudp);
> }
>
> static void __init pud_leaf_tests(unsigned long pfn, pgprot_t prot)
> @@ -431,8 +435,6 @@ static void __init pud_populate_tests(struct mm_struct *mm, pud_t *pudp,
> * This entry points to next level page table page.
> * Hence this must not qualify as pud_bad().
> */
> - pmd_clear(pmdp);
> - pud_clear(pudp);
Both entires are cleared before creating a fresh page table entry.
Why that is a problem.
> pud_populate(mm, pudp, pmdp);
> pud = READ_ONCE(*pudp);
> WARN_ON(pud_bad(pud));
> @@ -564,7 +566,6 @@ static void __init pmd_populate_tests(struct mm_struct *mm, pmd_t *pmdp,
> * This entry points to next level page table page.
> * Hence this must not qualify as pmd_bad().
> */
> - pmd_clear(pmdp);
Ditto.
> pmd_populate(mm, pmdp, pgtable);
> pmd = READ_ONCE(*pmdp);
> WARN_ON(pmd_bad(pmd));
>
next prev parent reply other threads:[~2020-08-13 5:29 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-12 6:33 [PATCH 01/16] powerpc/mm: Add DEBUG_VM WARN for pmd_clear Aneesh Kumar K.V
2020-08-12 6:33 ` [PATCH 02/16] debug_vm_pgtable/ppc64: Avoid setting top bits in radom value Aneesh Kumar K.V
2020-08-12 6:40 ` Christophe Leroy
2020-08-12 6:43 ` Aneesh Kumar K.V
2020-08-12 8:12 ` Anshuman Khandual
2020-08-12 8:25 ` Aneesh Kumar K.V
2020-08-12 6:33 ` [PATCH 03/16] debug_vm_pgtable/set_pte: Don't use set_pte_at to update an existing pte entry Aneesh Kumar K.V
2020-08-12 9:12 ` Anshuman Khandual
2020-08-12 9:22 ` Aneesh Kumar K.V
2020-08-12 6:33 ` [PATCH 04/16] debug_vm_pgtables/hugevmap: Use the arch helper to identify huge vmap support Aneesh Kumar K.V
2020-08-12 10:30 ` Anshuman Khandual
2020-08-12 6:33 ` [PATCH 05/16] debug_vm_pgtable/savedwrite: Enable savedwrite test with CONFIG_NUMA_BALANCING Aneesh Kumar K.V
2020-08-12 11:24 ` Anshuman Khandual
2020-08-12 6:33 ` [PATCH 06/16] debug_vm_pgtable/THP: Mark the pte entry huge before using set_pmd_at Aneesh Kumar K.V
2020-08-12 6:33 ` [PATCH 07/16] debug_vm_pgtable/THP: Mark the pte entry huge before using set_pud_at Aneesh Kumar K.V
2020-08-12 11:49 ` Anshuman Khandual
2020-08-12 6:33 ` [PATCH 08/16] debug_vm_pgtable/set_pmd: Don't use set_pmd_at to update an existing pmd entry Aneesh Kumar K.V
2020-08-12 12:46 ` Anshuman Khandual
2020-08-12 6:33 ` [PATCH 09/16] debug_vm_pgtable/set_pud: Don't use set_pud_at to update an existing pud entry Aneesh Kumar K.V
2020-08-12 12:46 ` Anshuman Khandual
2020-08-12 6:33 ` [PATCH 10/16] debug_vm_pgtable/thp: Use page table depost/withdraw with THP Aneesh Kumar K.V
2020-08-13 5:25 ` Anshuman Khandual
2020-08-13 6:38 ` Aneesh Kumar K.V
2020-08-12 6:33 ` [PATCH 11/16] debug_vm_pgtable/locks: Move non page table modifying test together Aneesh Kumar K.V
2020-08-12 6:33 ` [PATCH 12/16] debug_vm_pgtable/locks: Take correct page table lock Aneesh Kumar K.V
2020-08-12 6:33 ` [PATCH 13/16] debug_vm_pgtable/pmd_clear: Don't use pmd/pud_clear on pte entries Aneesh Kumar K.V
2020-08-13 5:27 ` Anshuman Khandual [this message]
2020-08-13 8:45 ` Aneesh Kumar K.V
2020-08-12 6:33 ` [PATCH 14/16] debug_vm_pgtable/hugetlb: Disable hugetlb test on ppc64 Aneesh Kumar K.V
2020-08-12 13:03 ` Anshuman Khandual
2020-08-12 13:16 ` Aneesh Kumar K.V
2020-08-12 13:34 ` Anshuman Khandual
2020-08-12 13:52 ` Aneesh Kumar K.V
2020-08-14 8:43 ` Anshuman Khandual
2020-08-19 6:54 ` Aneesh Kumar K.V
2020-08-12 6:33 ` [PATCH 15/16] debug_vm_pgtable/savedwrite: Use savedwrite test with protnone ptes Aneesh Kumar K.V
2020-08-12 13:06 ` Anshuman Khandual
2020-08-12 6:33 ` [PATCH 16/16] debug_vm_pgtable/ppc64: Add a variant of pfn_pte/pmd Aneesh Kumar K.V
2020-08-13 5:30 ` Anshuman Khandual
2020-08-13 6:37 ` Aneesh Kumar K.V
2020-08-14 8:29 ` Anshuman Khandual
2020-08-12 7:46 ` [PATCH 01/16] powerpc/mm: Add DEBUG_VM WARN for pmd_clear Anshuman Khandual
2020-08-12 8:27 ` Aneesh Kumar K.V
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