| Message ID | 20200812063358.369514-13-aneesh.kumar@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [01/16] powerpc/mm: Add DEBUG_VM WARN for pmd_clear | expand |
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)); >
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@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)); >>
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); 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); pmd_populate(mm, pmdp, pgtable); pmd = READ_ONCE(*pmdp); WARN_ON(pmd_bad(pmd));
pmd_clear() should not be used to clear pmd level pte entries. 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(-)