Re: [PATCH v5 2/3] mm: init: report memory auto-initialization features at boot time

Kaiwan N Billimoria
2019-06-05T02:59:07Z

On Tue, Jun 4, 2019 at 8:36 PM Alexander Potapenko <glider@google.com> wrote:
>
> On Tue, Jun 4, 2019 at 8:01 AM Kaiwan N Billimoria
> <kaiwan@kaiwantech.com> wrote:
> >
> > On Tue, Jun 4, 2019 at 8:44 AM Kees Cook <keescook@chromium.org> wrote:
> > >
> > > On Mon, Jun 03, 2019 at 11:24:49AM +0200, Alexander Potapenko wrote:
> > > > On Sat, Jun 1, 2019 at 3:18 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> > > > >
> > > > > On Wed, 29 May 2019 14:38:11 +0200 Alexander Potapenko <glider@google.com> wrote:
> > > > >
> > > > > > Print the currently enabled stack and heap initialization modes.
> > > > > >
> > > > > > The possible options for stack are:
> > > > > > - "all" for CONFIG_INIT_STACK_ALL;
> > > > > > - "byref_all" for CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL;
> > > > > > - "byref" for CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF;
> > > > > > - "__user" for CONFIG_GCC_PLUGIN_STRUCTLEAK_USER;
> > > > > > - "off" otherwise.
> > > > > >
> > > > > > Depending on the values of init_on_alloc and init_on_free boottime
> > > > > > options we also report "heap alloc" and "heap free" as "on"/"off".
> > > > >
> > > > > Why?
> > > > >
> > > > > Please fully describe the benefit to users so that others can judge the
> > > > > desirability of the patch. And so they can review it effectively, etc.
> > > > I'm going to update the description with the following passage:
> > > >
> > > > Print the currently enabled stack and heap initialization modes.
> > > >
> > > > Stack initialization is enabled by a config flag, while heap
> > > > initialization is configured at boot time with defaults being set
> > > > in the config. It's more convenient for the user to have all information
> > > > about these hardening measures in one place.
> > > >
> > > > Does this make sense?
> > > > > Always!
> > > > >
> > > > > > In the init_on_free mode initializing pages at boot time may take some
> > > > > > time, so print a notice about that as well.
> > > > >
> > > > > How much time?
> > > > I've seen pauses up to 1 second, not actually sure they're worth a
> > > > separate line in the log.
> > > > Kees, how long were the delays in your case?
> > >
> > > I didn't measure it, but I think it was something like 0.5 second per GB.
> > > I noticed because normally boot flashes by. With init_on_free it pauses
> > > for no apparent reason, which is why I suggested the note. (I mean *I*
> > > knew why it was pausing, but it might surprise someone who sets
> > > init_on_free=1 without really thinking about what's about to happen at
> > > boot.)
> >
> > (Pardon the gmail client)
> > How about:
> > - if (want_init_on_free())
> > - pr_info("Clearing system memory may take some time...\n");
> > + if (want_init_on_free())
> > + pr_info("meminit: clearing system memory may take some
> > time...\n");
> Yes, adding a prefix may give the users better understanding of who's
> clearing the memory.
> We should stick to the same prefix as before though, i.e. "mem auto-init"

True, agreed.
--
Kaiwan