On 8/13/20 10:57 AM, Anshuman Khandual wrote:
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.
pmd_clear is implemented such that we don't use that to clear a huge pte
entry. We use pmdp_huge_get_and_clear() for that. Hence we have check in
pmd_clear which add a WARN if we find a _PAGE_PTE set on the entry.
In the test we follow a hugepmd usage with a pmd_clear. We should
instead at the end of the advanced pmd test use pmdp_huge_get_and_clear().
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
---
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));
