Re: [RFC]: mm,power: introduce MADV_WIPEONSUSPEND

Jann Horn
2020-07-03T22:53:34Z

On Sat, Jul 4, 2020 at 12:34 AM Pavel Machek <pavel@ucw.cz> wrote:
> On Fri 2020-07-03 15:29:22, Jann Horn wrote:
> > On Fri, Jul 3, 2020 at 1:30 PM Michal Hocko <mhocko@kernel.org> wrote:
> > > On Fri 03-07-20 10:34:09, Catangiu, Adrian Costin wrote:
> > > > This patch adds logic to the kernel power code to zero out contents of
> > > > all MADV_WIPEONSUSPEND VMAs present in the system during its transition
> > > > to any suspend state equal or greater/deeper than Suspend-to-memory,
> > > > known as S3.
> > >
> > > How does the application learn that its memory got wiped? S2disk is an
> > > async operation and it can happen at any time during the task execution.
> > > So how does the application work to prevent from corrupted state - e.g.
> > > when suspended between two memory loads?
> >
> > You can do it seqlock-style, kind of - you reserve the first byte of
> > the page or so as a "is this page initialized" marker, and after every
> > read from the page, you do a compiler barrier and check whether that
> > byte has been
>
> That would also need smp cpu barriers, and guarantee that first byte
> is always ... cleared first, and matching barriers in kernel space,
> too, no?

Not if it happens in the guts of the suspend stuff, when userspace is
frozen, I think?