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

[Guo Ren]

On Mon, Jul 3, 2023 at 9:07 PM chenjiahao (C) <chenjiahao16@xxxxxxxxxx> wrote:
>
>
> On 2023/7/1 21:45, Guo Ren wrote:
> > 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/
>
> 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.
Yes, the pud of sv57 is not the pgd entries, so you didn't get problem.

>
>
> 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
> >>
> >



-- 
Best Regards
 Guo Ren