Re: [PATCH v3 00/12] mm/kasan: make kasan=on|off work for all three modes

Andrey Konovalov
2025-09-06T13:25:31Z

On Fri, Sep 5, 2025 at 10:34 PM Andrey Konovalov <andreyknvl@gmail.com> wrote:
>
> Baoquan, I'd be in favor of implementing kasan.vmalloc=off instead of
> kasan=off. This seems to both (almost) solve the RAM overhead problem
> you're having (AFAIU) and also seems like a useful feature on its own
> (similar to CONFIG_KASAN_VMALLOC=n but via command-line). The patches
> to support kasan.vmalloc=off should also be orthogonal to the
> Sabyrzhan's series.
>
> If you feel strongly that the ~1/8th RAM overhead (coming from the
> physmap shadow and the slab redzones) is still unacceptable for your
> use case (noting that the performance overhead (and the constant
> silent detection of false-positive bugs) would still be there), I
> think you can proceed with your series (unless someone else is
> against).

Hm, just realized that kasan.vmalloc=off would probably break if
CONFIG_VMAP_STACK is enabled: read-only shadow for vmalloc =>
read-only shadow for stacks => stack instrumentation will try writing
into read-only shadow and crash.

So I wonder if there's a way to avoid the lazy vmap freeing to deal
with the RAM overhead.