linux-kernel - Re: [RFC PATCH] ARM: Support allocating crashkernel above 4G for LPAE

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Message-ID: <Zqy8lwZM2Z6RlV5H@shell.armlinux.org.uk>
Date: Fri, 2 Aug 2024 12:01:43 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Jinjie Ruan <ruanjinjie@...wei.com>
Cc: bhe@...hat.com, akpm@...ux-foundation.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] ARM: Support allocating crashkernel above 4G for LPAE

On Fri, Aug 02, 2024 at 05:25:10PM +0800, Jinjie Ruan wrote:
> As ARM LPAE feature support accessing memory beyond the 4G limit, define
> HAVE_ARCH_CRASHKERNEL_RESERVATION_HIGH macro to support reserving crash
> memory above 4G for ARM32 LPAE.
> 
> No test because there is no LPAE ARM32 hardware.

Why are you submitting patches for features you can't test?

I'm not going to apply this without it being properly tested, because I
don't believe that this will work in the generic case.

If the crash kernel is located in memory outside of the lower 4GiB of
address space, and there is no alias within physical address space
for that memory, then there is *no* *way* for such a kernel to boot.

So, right now I believe this patch to be *fundamentally* wrong.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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