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

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Message-ID: <a1bc7a9d-817d-49cc-b7f1-79a900090136@gmail.com>
Date: Tue, 22 Jul 2025 01:18:52 +0200
From: Andrey Ryabinin <ryabinin.a.a@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
 Sabyrzhan Tasbolatov <snovitoll@...il.com>
Cc: hca@...ux.ibm.com, christophe.leroy@...roup.eu, andreyknvl@...il.com,
 agordeev@...ux.ibm.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
Subject: Re: [PATCH v3 01/12] lib/kasan: introduce CONFIG_ARCH_DEFER_KASAN
 option



On 7/18/25 12:10 AM, Andrew Morton 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?

After looking a bit, it breaks UM and probably LoongArch too.
I'd say it needs more work and not ready even for mm-new.