Re: [PATCH 1/3] mm, page_alloc: do not rely on the order of page_poison and init_on_alloc/free parameters

[Vlastimil Babka]

On 10/27/20 10:03 AM, David Hildenbrand wrote:
> On 26.10.20 18:33, Vlastimil Babka wrote:
> > Enabling page_poison=1 together with init_on_alloc=1 or init_on_free=1 produces
> > a warning in dmesg that page_poison takes precendence. However, as these
> > warnings are printed in early_param handlers for init_on_alloc/free, they are
> > not printed if page_poison is enabled later on the command line (handlers are
> > called in the order of their parameters), or when init_on_alloc/free is always
> > enabled by the respective config option - before the page_poison early param
> > handler is called, it is not considered to be enabled. This is inconsistent.
> >
> > We can remove the dependency on order by making the init_on_* parameters only
> > set a boolean variable, and postponing the evaluation after all early params
> > have been processed. Introduce a new init_mem_debugging() function for that,
> > and move the related debug_pagealloc processing there as well.
>
> init_mem_debugging() is somewhat sub-optimal - init_on_alloc=1 or
> init_on_free=1 are rather security hardening mechanisms.

Well yeah, init_mem_debugging_and_hardening()?

> ... I wondered if this could be the place to initialize any kind of mm
> parameters in the future. Like init_mem_params() or so.

Maybe. In practice you often find out that different things have to be hooked in 
different points of the init process, and a single function might not be enough. 
I tried to group stuff that's really inter-related and can be initialized at the 
same time.

> > As a result init_mem_debugging() knows always accurately if init_on_* and/or
> > page_poison options were enabled. Thus we can also optimize want_init_on_alloc()
> > and want_init_on_free(). We don't need to check page_poisoning_enabled() there,
> > we can instead not enable the init_on_* tracepoint at all, if page poisoning is
> > enabled. This results in a simpler and more effective code.
>
> LGTM
>
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

Thanks!