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

Mike Rapoport
2023-01-26T09:26:58Z

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
>
>