Re: [PATCH] mm/damon: validate addr_unit to be power of 2

[Liew Rui Yan <aethernet65535@gmail.com>]

Hi SeongJae,

On Sun, 29 Mar 2026 08:15:07 -0700 SeongJae Park <sj@kernel.org> wrote:

> On Sun, 29 Mar 2026 15:51:07 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:
> [...]
> > To confirm, are you suggesting something like the first approach [1]?
> > 
> >     if (input_addr_unit < PAGE_SIZE && !is_power_of_2(input_addr_unit))
> >         return -EINVAL;
> 
> Yes.  But the real constraint is min_region_sz, so testing it would be more
> simple and effective.  E.g.,
> 
> 	if (!is_power_of_2(param_ctx->min_region_sz))
> 		return -EINVAL;
> > 
> > [1] https://lore.kernel.org/20260325071709.9699-1-aethernet65535@gmail.com

Thank you for the example.

The 'param_ctx' you mentioned confused me for a moment, as it doesn't
exist in the current addr_unit_store(). But I assume you are suggesting
that we should validate the result of 'min_region_sz' rather than the
'addr_unit' itself, and this check should happen within the
addr_unit_store() callback.

So, would something like this in addr_uint_store() be what you expect?

    if (!input_addr_unit)
        return -EINVAL;

    min_region_sz = max(PAGE_SIZE / input_addr_unit, 1);
    if (!is_power_of_2(min_region_sz))
        return -EINVAL;

This keeps the fix local to the modules, and directly enforces the
power-of-2 constraint on the actual monitoring granularity.

Best regards,
Rui Yan