linux-kernel - Re: [PATCH -next v6 0/2] support allocating crashkernel above 4G explicitly on riscv

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Date:   Mon, 3 Jul 2023 21:07:15 +0800
From:   "chenjiahao (C)" <chenjiahao16@...wei.com>
To:     Guo Ren <guoren@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
        <kexec@...ts.infradead.org>, <linux-doc@...r.kernel.org>,
        <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <conor.dooley@...rochip.com>, <heiko@...ech.de>,
        <bjorn@...osinc.com>, <alex@...ti.fr>, <akpm@...ux-foundation.org>,
        <atishp@...osinc.com>, <bhe@...hat.com>,
        <thunder.leizhen@...wei.com>, <horms@...nel.org>
Subject: Re: [PATCH -next v6 0/2] support allocating crashkernel above 4G
 explicitly on riscv


On 2023/7/1 21:45, Guo Ren wrote:
> On Sat, Jul 1, 2023 at 5:12 PM Chen Jiahao <chenjiahao16@...wei.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=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
>>
>> Following test cases have been performed as expected:
>> 1) crashkernel=256M                          //low=256M
>> 2) crashkernel=1G                            //low=1G
> 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/

I have tested on QEMU with sv57 mmu, so it seems the synchronization problem
was not reproduce when reserving 1G memory and loading the capture kernel.


Thanks,
Jiahao

>
>> 3) crashkernel=4G                            //high=4G, low=128M(default)
>> 4) crashkernel=4G crashkernel=256M,high      //high=4G, low=128M(default), high is ignored
>> 5) crashkernel=4G crashkernel=256M,low       //high=4G, low=128M(default), low is ignored
>> 6) crashkernel=4G,high                       //high=4G, low=128M(default)
>> 7) crashkernel=256M,low                      //low=0M, invalid
>> 8) crashkernel=4G,high crashkernel=256M,low  //high=4G, low=256M
>> 9) crashkernel=4G,high crashkernel=4G,low    //high=0M, low=0M, invalid
>> 10) crashkernel=512M@...0000000              //low=512M
>>
>> Changes since [v6]:
>> 1. Introduce the "high" flag to mark whether "crashkernel=X,high"
>>     is passed. Fix the retrying logic between "crashkernel=X,high"
>>     case and others when the first allocation attempt fails.
>>
>> Changes since [v5]:
>> 1. Update the crashkernel allocation logic when crashkernel=X,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=size@...set 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=X,[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
>>
>