linux-kernel - Re: [PATCH v2 00/12] mm/kasan: make kasan=on|off work for all three modes

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Message-ID: <CA+fCnZcdSDEZvRSxEnogBMCFg1f-PK7PKx0KB_1SA0saY6-21g@mail.gmail.com>
Date: Sat, 16 Aug 2025 06:50:06 +0200
From: Andrey Konovalov <andreyknvl@...il.com>
To: Baoquan He <bhe@...hat.com>
Cc: linux-mm@...ck.org, ryabinin.a.a@...il.com, glider@...gle.com, 
	dvyukov@...gle.com, vincenzo.frascino@....com, akpm@...ux-foundation.org, 
	kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, 
	kexec@...ts.infradead.org, sj@...nel.org, lorenzo.stoakes@...cle.com, 
	elver@...gle.com, snovitoll@...il.com
Subject: Re: [PATCH v2 00/12] mm/kasan: make kasan=on|off work for all three modes

On Thu, Aug 14, 2025 at 10:56 AM Baoquan He <bhe@...hat.com> wrote:
>
> Ah, I got what you mean. We probably are saying different things.
>
> In order to record memory content of a corrupted kernel, we need reserve
> a memory region during bootup of a normal kernel (usually called 1st
> kernel) via kernel parameter crashkernel=nMB in advance. Then load
> kernel into the crashkernel memory region, that means the region is not
> usable for 1st kernel. When 1st kernel collapsed, we stop the 1st kernel
> cpu/irq and warmly switch to the loaded kernel in the crashkernel memory
> region (usually called kdump kernel). In kdump kernel, it boots up and
> enable necessary features to read out the 1st kernel's memory content,
> we usually use user space tool like makeudmpfile to filter out unwanted
> memory content.
>
> So this patchset intends to disable KASAN to decrease the crashkernel
> meomry value because crashkernel is not usable for 1st kernel. As for
> shadow memory of 1st kernel, we need recognize it and filter it away
> in makedumpfile.

Ah, I see, thank you for the explanation!

So kdump kernel runs with the amount of RAM specified by crashkernel=.
And KASAN's shadow memory increases RAM usage, which means
crashkernel= needs to be set to a higher value for KASAN kernels. Is
my understanding of the problem correct?