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

[Suren Baghdasaryan <surenb@xxxxxxxxxx>]

On Wed, Jan 25, 2023 at 9:08 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Wed 25-01-23 08:57:48, Suren Baghdasaryan wrote:
> > On Wed, Jan 25, 2023 at 1:38 AM 'Michal Hocko' via kernel-team
> > <kernel-team@xxxxxxxxxxx> wrote:
> > >
> > > On Wed 25-01-23 00:38:49, 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.
> > >
> > > Those BUG_ONs scream to much IMHO. KSM is an MM internal code so I
> > > gueess we should be willing to trust it.
> >
> > Yes, but I really want to prevent an indirect misuse since it was not
> > easy to find these. If you feel strongly about it I will remove them
> > or if you have a better suggestion I'm all for it.
>
> You can avoid that by making flags inaccesible directly, right?

Ah, you mean Peter's suggestion of using __private? I guess that would
cover it. I'll drop these BUG_ONs in the next version. Thanks!

>
> --
> Michal Hocko
> SUSE Labs