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.ku...@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));
>
