linux-kernel - Re: [PATCH v3 01/12] lib/kasan: introduce CONFIG_ARCH_DEFER

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Message-ID: <CACzwLxgyd9yd3ah=LK93Bn7SwAy7H1Hhi=ncFzZYUs+6YGEqvg@mail.gmail.com>
Date: Fri, 18 Jul 2025 13:05:32 +0500
From: Sabyrzhan Tasbolatov <snovitoll@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: hca@...ux.ibm.com, christophe.leroy@...roup.eu, andreyknvl@...il.com, 
	agordeev@...ux.ibm.com, ryabinin.a.a@...il.com, glider@...gle.com, 
	dvyukov@...gle.com, kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, 
	loongarch@...ts.linux.dev, linuxppc-dev@...ts.ozlabs.org, 
	linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org, 
	linux-um@...ts.infradead.org, linux-mm@...ck.org, 
	Peter Zijlstra <peterz@...radead.org>, Johannes Berg <johannes@...solutions.net>
Subject: Re: [PATCH v3 01/12] lib/kasan: introduce CONFIG_ARCH_DEFER_KASAN option

On Fri, Jul 18, 2025 at 3:10 AM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Thu, 17 Jul 2025 19:27:21 +0500 Sabyrzhan Tasbolatov <snovitoll@...il.com> wrote:
>
> > Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures that need
> > to defer KASAN initialization until shadow memory is properly set up.
> >
> > Some architectures (like PowerPC with radix MMU) need to set up their
> > shadow memory mappings before KASAN can be safely enabled, while others
> > (like s390, x86, arm) can enable KASAN much earlier or even from the
> > beginning.
> >
> > This option allows us to:
> > 1. Use static keys only where needed (avoiding overhead)
> > 2. Use compile-time constants for arch that don't need runtime checks
> > 3. Maintain optimal performance for both scenarios
> >
> > Architectures that need deferred KASAN should select this option.
> > Architectures that can enable KASAN early will get compile-time
> > optimizations instead of runtime checks.
>
> Looks nice and appears quite mature.  I'm reluctant to add it to mm.git
> during -rc6, especially given the lack of formal review and ack tags.
>
> But but but, that's what the mm-new branch is for.  I guess I'll add it
> to get some additional exposure, but whether I'll advance it into
> mm-unstable/linux-next for this cycle is unclear.
>
> What do you (and others) think?

Thanks for the positive feedback!
Adding it to mm-new for additional exposure would be great.
Given the complexity of this cross-architecture change,
I think of taking the conservative approach of:
1. mm-new branch for exposure and review collection
2. Advancing to mm-unstable/linux-next only after we get proper acks from
    KASAN maintainers/reviewers, at least.

The series has been thoroughly tested by me - compiled all affected arch and
ran QEMU on arm64, x86 with KUnits.

+ Forgot to add in CC Johannes Berg, Peter Zijlstra who commented in v1.
https://lore.kernel.org/all/20250625095224.118679-1-snovitoll@gmail.com/