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

[Guo Ren]

On Sat, Jul 1, 2023 at 5:12 PM Chen Jiahao <chenjiahao16@xxxxxxxxxx> 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@xxxxxxxxxx/

> 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
>


-- 
Best Regards
 Guo Ren