On 8/20/20 8:02 PM, Christophe Leroy wrote:

Le 19/08/2020 à 15:01, Aneesh Kumar K.V a écrit :

quoted

set_pte_at() should not be used to set a pte entry at locations that
already holds a valid pte entry. Architectures like ppc64 don't do TLB
invalidate in set_pte_at() and hence expect it to be used to set 
locations
that are not a valid PTE.

Signed-off-by: Aneesh Kumar K.V <redacted>
---
  mm/debug_vm_pgtable.c | 35 +++++++++++++++--------------------
  1 file changed, 15 insertions(+), 20 deletions(-)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 76f4c713e5a3..9c7e2c9cfc76 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c

@@ -74,15 +74,18 @@ static void __init pte_advanced_tests(struct 

mm_struct *mm,
  {
      pte_t pte = pfn_pte(pfn, prot);
+    /*
+     * Architectures optimize set_pte_at by avoiding TLB flush.
+     * This requires set_pte_at to be not used to update an
+     * existing pte entry. Clear pte before we do set_pte_at
+     */
+
      pr_debug("Validating PTE advanced\n");
      pte = pfn_pte(pfn, prot);
      set_pte_at(mm, vaddr, ptep, pte);
      ptep_set_wrprotect(mm, vaddr, ptep);
      pte = ptep_get(ptep);
      WARN_ON(pte_write(pte));
-
-    pte = pfn_pte(pfn, prot);
-    set_pte_at(mm, vaddr, ptep, pte);
      ptep_get_and_clear(mm, vaddr, ptep);
      pte = ptep_get(ptep);
      WARN_ON(!pte_none(pte));

@@ -96,13 +99,11 @@ static void __init pte_advanced_tests(struct 

mm_struct *mm,
      ptep_set_access_flags(vma, vaddr, ptep, pte, 1);
      pte = ptep_get(ptep);
      WARN_ON(!(pte_write(pte) && pte_dirty(pte)));
-
-    pte = pfn_pte(pfn, prot);
-    set_pte_at(mm, vaddr, ptep, pte);
      ptep_get_and_clear_full(mm, vaddr, ptep, 1);
      pte = ptep_get(ptep);
      WARN_ON(!pte_none(pte));
+    pte = pfn_pte(pfn, prot);
      pte = pte_mkyoung(pte);
      set_pte_at(mm, vaddr, ptep, pte);
      ptep_test_and_clear_young(vma, vaddr, ptep);

@@ -164,9 +165,6 @@ static void __init pmd_advanced_tests(struct 

mm_struct *mm,
      pmdp_set_wrprotect(mm, vaddr, pmdp);
      pmd = READ_ONCE(*pmdp);
      WARN_ON(pmd_write(pmd));
-
-    pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
-    set_pmd_at(mm, vaddr, pmdp, pmd);
      pmdp_huge_get_and_clear(mm, vaddr, pmdp);
      pmd = READ_ONCE(*pmdp);
      WARN_ON(!pmd_none(pmd));

@@ -180,13 +178,11 @@ static void __init pmd_advanced_tests(struct 

mm_struct *mm,
      pmdp_set_access_flags(vma, vaddr, pmdp, pmd, 1);
      pmd = READ_ONCE(*pmdp);
      WARN_ON(!(pmd_write(pmd) && pmd_dirty(pmd)));
-
-    pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
-    set_pmd_at(mm, vaddr, pmdp, pmd);
      pmdp_huge_get_and_clear_full(vma, vaddr, pmdp, 1);
      pmd = READ_ONCE(*pmdp);
      WARN_ON(!pmd_none(pmd));
+    pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
      pmd = pmd_mkyoung(pmd);
      set_pmd_at(mm, vaddr, pmdp, pmd);
      pmdp_test_and_clear_young(vma, vaddr, pmdp);

@@ -283,18 +279,10 @@ static void __init pud_advanced_tests(struct 

mm_struct *mm,
      WARN_ON(pud_write(pud));
  #ifndef __PAGETABLE_PMD_FOLDED

Same as below, once set_put_at() is gone, I don't think this #ifndef 
__PAGETABLE_PMD_FOLDED is still need, should be possible to replace by 
'if (mm_pmd_folded())'

I would skip that change in this series because I still haven't worked 
out what it means to have FOLDED PMD with 
CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD.


We should probably push that as a cleanup later and somebody who can 
test that config can do that? Currently i can't boot ppc64 with 
DBUG_VM_PGTABLE enabled on ppc64 because it is all buggy w.r.t rules.

-aneesh