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

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Message-ID: <6c0a45c3-08a2-f889-9e66-ab8aff66ae8c@huawei.com>
Date: Mon, 5 Aug 2024 09:23:50 +0800
From: Jinjie Ruan <ruanjinjie@...wei.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
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 2024/8/2 19:01, Russell King (Oracle) wrote:
> 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.

I'm sorry that I released this patch without testing it. I actually
intended to bring up this issue for discussion. If anyone has the
environment to test it, that would be great. In the meantime, we could
have a discussion on the significance and relevance of this approach.

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