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!
