Re: [PATCH 13/16] debug_vm_pgtable/pmd_clear: Don't use pmd/pud_clear on pte entries
From: Anshuman Khandual <hidden>
Date: 2020-08-13 05:28:17
Also in:
linuxppc-dev
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.
quoted hunk ↗ jump to hunk
Signed-off-by: Aneesh Kumar K.V <redacted> --- 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.
quoted hunk ↗ jump to hunk
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));