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    SubjectRe: [PATCH v2 4/6] mm: replace vma->vm_flags indirect modification in ksm_madvise
    On Wed, Jan 25, 2023 at 12:38:49AM -0800, Suren Baghdasaryan wrote:
    > 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@google.com>

    Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>

    > ---
    > 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
    >
    >

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