On Wed, Jan 25, 2023 at 03:35:52PM -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.
>
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> arch/powerpc/kvm/book3s_hv_uvmem.c | 5 ++++-
> arch/s390/mm/gmap.c | 5 ++++-
> 2 files changed, 8 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);
Add a comment on why the vm_flags are copied in case someone "optimises"
this in the future? Something like
/* Copy vm_flags to avoid any partial modifications in ksm_madvise. */
>
> 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);
Same.
Not necessary as such as there are few users of ksm_madvise and I doubt
it'll introduce new surprises.
With or without the comment;
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
--
Mel Gorman
SUSE Labs
