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

chenjiahao (C)
2023-07-03T13:07:25Z

On 2023/7/1 21:45, Guo Ren wrote:
> On Sat, Jul 1, 2023 at 5:12 PM 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=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@0xd0000000 //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@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=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
>>
>