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References: <20230701171138.1491206-1-chenjiahao16@huawei.com>
In-Reply-To: <20230701171138.1491206-1-chenjiahao16@huawei.com>
From:   Guo Ren <guoren@kernel.org>
Date:   Sat, 1 Jul 2023 21:45:00 +0800
Message-ID: <CAJF2gTSPaBvB_CsmN5m91AVXwXB37j2qvyCP3VqALxHwNcGeTg@mail.gmail.com>
Subject: Re: [PATCH -next v6 0/2] support allocating crashkernel above 4G
 explicitly on riscv
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, heiko@sntech.de, bjorn@rivosinc.com,
        alex@ghiti.fr, akpm@linux-foundation.org, atishp@rivosinc.com,
        bhe@redhat.com, thunder.leizhen@huawei.com, horms@kernel.org
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On Sat, Jul 1, 2023 at 5:12=E2=80=AFPM Chen Jiahao <chenjiahao16@huawei.com=
> 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=3DX,[high=
,low].
>
> One can reserve the crash kernel from high memory above DMA zone range
> by explicitly passing "crashkernel=3DX,high"; or reserve a memory range
> below 4G with "crashkernel=3DX,low". Besides, there are few rules need
> to take notice:
> 1. "crashkernel=3DX,[high,low]" will be ignored if "crashkernel=3Dsize"
>    is specified.
> 2. "crashkernel=3DX,low" is valid only when "crashkernel=3DX,high" is pas=
sed
>    and there is enough memory to be allocated under 4G.
> 3. When allocating crashkernel above 4G and no "crashkernel=3DX,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
>
> Following test cases have been performed as expected:
> 1) crashkernel=3D256M                          //low=3D256M
> 2) crashkernel=3D1G                            //low=3D1G
Have you tried 1GB memory? we found a pud mapping problem on Sv39 of kexec,=
 See:
https://lore.kernel.org/linux-riscv/20230629082032.3481237-1-guoren@kernel.=
org/

> 3) crashkernel=3D4G                            //high=3D4G, low=3D128M(de=
fault)
> 4) crashkernel=3D4G crashkernel=3D256M,high      //high=3D4G, low=3D128M(=
default), high is ignored
> 5) crashkernel=3D4G crashkernel=3D256M,low       //high=3D4G, low=3D128M(=
default), low is ignored
> 6) crashkernel=3D4G,high                       //high=3D4G, low=3D128M(de=
fault)
> 7) crashkernel=3D256M,low                      //low=3D0M, invalid
> 8) crashkernel=3D4G,high crashkernel=3D256M,low  //high=3D4G, low=3D256M
> 9) crashkernel=3D4G,high crashkernel=3D4G,low    //high=3D0M, low=3D0M, i=
nvalid
> 10) crashkernel=3D512M@0xd0000000              //low=3D512M
>
> Changes since [v6]:
> 1. Introduce the "high" flag to mark whether "crashkernel=3DX,high"
>    is passed. Fix the retrying logic between "crashkernel=3DX,high"
>    case and others when the first allocation attempt fails.
>
> Changes since [v5]:
> 1. Update the crashkernel allocation logic when crashkernel=3DX,high
>    is specified. In this case, region above 4G will directly get
>    reserved as crashkernel, rather than trying lower 32bit allocation
>    first.
>
> Changes since [v4]:
> 1. Update some imprecise code comments for cmdline parsing.
>
> Changes since [v3]:
> 1. Update to print warning and return explicitly on failure when
>    crashkernel=3Dsize@offset is specified. Not changing the result
>    in this case but making the logic more straightforward.
> 2. Some minor cleanup.
>
> Changes since [v2]:
> 1. Update the allocation logic to ensure the high crashkernel
>    region is reserved strictly above dma32_phys_limit.
> 2. Clean up some minor format problems.
>
> Chen Jiahao (2):
>   riscv: kdump: Implement crashkernel=3DX,[high,low]
>   docs: kdump: Update the crashkernel description for riscv
>
>  .../admin-guide/kernel-parameters.txt         | 15 ++--
>  arch/riscv/kernel/setup.c                     |  5 ++
>  arch/riscv/mm/init.c                          | 84 +++++++++++++++++--
>  3 files changed, 90 insertions(+), 14 deletions(-)
>
> --
> 2.34.1
>


--=20
Best Regards
 Guo Ren