[PATCH v2 4/6] mm: replace vma->vm_flags indirect modification in ksm_madvise

[Suren Baghdasaryan <surenb@xxxxxxxxxx>]

Replace indirect modifications to vma->vm_flags with calls to modifier
functions to be able to track flag changes and to keep vma locking
correctness. Add a BUG_ON check in ksm_madvise() to catch indirect
vm_flags modification attempts.

Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
 arch/powerpc/kvm/book3s_hv_uvmem.c | 5 ++++-
 arch/s390/mm/gmap.c                | 5 ++++-
 mm/khugepaged.c                    | 2 ++
 mm/ksm.c                           | 2 ++
 4 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c 
b/arch/powerpc/kvm/book3s_hv_uvmem.c
index 1d67baa5557a..325a7a47d348 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -393,6 +393,7 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
 {
        unsigned long gfn = memslot->base_gfn;
        unsigned long end, start = gfn_to_hva(kvm, gfn);
+       unsigned long vm_flags;
        int ret = 0;
        struct vm_area_struct *vma;
        int merge_flag = (merge) ? MADV_MERGEABLE : MADV_UNMERGEABLE;
@@ -409,12 +410,14 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
                        ret = H_STATE;
                        break;
                }
+               vm_flags = vma->vm_flags;
                ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
-                         merge_flag, &vma->vm_flags);
+                         merge_flag, &vm_flags);
                if (ret) {
                        ret = H_STATE;
                        break;
                }
+               reset_vm_flags(vma, vm_flags);
                start = vma->vm_end;
        } while (end > vma->vm_end);
 
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 3a695b8a1e3c..d5eb47dcdacb 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -2587,14 +2587,17 @@ int gmap_mark_unmergeable(void)
 {
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
+       unsigned long vm_flags;
        int ret;
        VMA_ITERATOR(vmi, mm, 0);
 
        for_each_vma(vmi, vma) {
+               vm_flags = vma->vm_flags;
                ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
-                                 MADV_UNMERGEABLE, &vma->vm_flags);
+                                 MADV_UNMERGEABLE, &vm_flags);
                if (ret)
                        return ret;
+               reset_vm_flags(vma, vm_flags);
        }
        mm->def_flags &= ~VM_MERGEABLE;
        return 0;
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 8abc59345bf2..76b24cd0c179 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -354,6 +354,8 @@ struct attribute_group khugepaged_attr_group = {
 int hugepage_madvise(struct vm_area_struct *vma,
                     unsigned long *vm_flags, int advice)
 {
+       /* vma->vm_flags can be changed only using modifier functions */
+       BUG_ON(vm_flags == &vma->vm_flags);
        switch (advice) {
        case MADV_HUGEPAGE:
 #ifdef CONFIG_S390
diff --git a/mm/ksm.c b/mm/ksm.c
index 04f1c8c2df11..992b2be9f5e6 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2573,6 +2573,8 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long 
start,
        struct mm_struct *mm = vma->vm_mm;
        int err;
 
+       /* vma->vm_flags can be changed only using modifier functions */
+       BUG_ON(vm_flags == &vma->vm_flags);
        switch (advice) {
        case MADV_MERGEABLE:
                /*
-- 
2.39.1