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Date:   Fri, 7 Apr 2023 14:05:17 +0200
From:   Simon Horman <horms@kernel.org>
To:     Chen Jiahao <chenjiahao16@huawei.com>
Cc:     linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
        kexec@lists.infradead.org, linux-doc@vger.kernel.org,
        paul.walmsley@sifive.com, palmer@dabbelt.com,
        conor.dooley@microchip.com, guoren@kernel.org, heiko@sntech.de,
        bjorn@rivosinc.com, alex@ghiti.fr, akpm@linux-foundation.org,
        atishp@rivosinc.com, bhe@redhat.com, thunder.leizhen@huawei.com
Subject: Re: [PATCH -next v3 0/2] support allocating crashkernel above 4G
 explicitly on riscv
Message-ID: <ZDAG/Re2CbuMFXOg@kernel.org>
References: <20230406220206.3067006-1-chenjiahao16@huawei.com>
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On Fri, Apr 07, 2023 at 06:02:04AM +0800, Chen Jiahao wrote:
> On riscv, the current crash kernel allocation logic is trying to
> allocate within 32bit addressible memory region by default, if
> failed, try to allocate without 4G restriction.
> 
> In need of saving DMA zone memory while allocating a relatively large
> crash kernel region, allocating the reserved memory top down in
> high memory, without overlapping the DMA zone, is a mature solution.
> Hence this patchset introduces the parameter option crashkernel=X,[high,low].
> 
> One can reserve the crash kernel from high memory above DMA zone range
> by explicitly passing "crashkernel=X,high"; or reserve a memory range
> below 4G with "crashkernel=X,low". Besides, there are few rules need
> to take notice:
> 1. "crashkernel=X,[high,low]" will be ignored if "crashkernel=size"
>    is specified.
> 2. "crashkernel=X,low" is valid only when "crashkernel=X,high" is passed
>    and there is enough memory to be allocated under 4G.
> 3. When allocating crashkernel above 4G and no "crashkernel=X,low" is
>    specified, a 128M low memory will be allocated automatically for
>    swiotlb bounce buffer.
> See Documentation/admin-guide/kernel-parameters.txt for more information.
> 
> To verify loading the crashkernel, adapted kexec-tools is attached below:
> https://github.com/chenjh005/kexec-tools/tree/build-test-riscv-v2

Are you planning to submit the kexec-tools patches too?