Subject: Re: [PATCH v13 0/8] support reserving crashkernel above 4G on arm64 kdump

From: Baoquan He <[email-masked]>
Date: Wed, 11 Nov 2020 11:01:36 +0800

Hi Zhou, Bhupesh

On 10/31/20 at 03:44pm, Chen Zhou wrote:
> There are following issues in arm64 kdump:
> 1. We use crashkernel=X to reserve crashkernel below 4G, which
> will fail when there is no enough low memory.
> 2. If reserving crashkernel above 4G, in this case, crash dump
> kernel will boot failure because there is no low memory available
> for allocation.
> 3. Since commit 1a8e1cef7603 ("arm64: use both ZONE_DMA and ZONE_DMA32"),
> if the memory reserved for crash dump kernel falled in ZONE_DMA32,
> the devices in crash dump kernel need to use ZONE_DMA will alloc
> fail.

I went through this patchset, mainly the x86 related and generic
changes, the changes look great and no risk. And I know Bhupesh is
following up this and helping review, thanks, both.

So you have also tested crashkernel reservation on x86_64, with the
normal reservation, and high/low reservation, it is working well,
right? Asking this because I didn't see the test result description, and
just note it.

Thanks
Baoquan

> 
> To solve these issues, change the behavior of crashkernel=X.
> crashkernel=X tries low allocation in DMA zone (or the DMA32 zone if
> CONFIG_ZONE_DMA is disabled), and fall back to high allocation if it fails.
> 
> We can also use "crashkernel=X,high" to select a high region above
> DMA zone, which also tries to allocate at least 256M low memory in
> DMA zone automatically (or the DMA32 zone if CONFIG_ZONE_DMA is disabled).
> "crashkernel=Y,low" can be used to allocate specified size low memory.
> 
> When reserving crashkernel in high memory, some low memory is reserved
> for crash dump kernel devices. So there may be two regions reserved for
> crash dump kernel.
> In order to distinct from the high region and make no effect to the use
> of existing kexec-tools, rename the low region as "Crash kernel (low)",
> and pass the low region by reusing DT property
> "linux,usable-memory-range". We made the low memory region as the last
> range of "linux,usable-memory-range" to keep compatibility with existing
> user-space and older kdump kernels.
> 
> Besides, we need to modify kexec-tools:
> arm64: support more than one crash kernel regions(see [1])
> 
> Another update is document about DT property 'linux,usable-memory-range':
> schemas: update 'linux,usable-memory-range' node schema(see [2])
> 
> This patchset contains the following eight patches:
> 0001-x86-kdump-replace-the-hard-coded-alignment-with-macr.patch
> 0002-x86-kdump-make-the-lower-bound-of-crash-kernel-reser.patch
> 0003-x86-kdump-use-macro-CRASH_ADDR_LOW_MAX-in-functions-.patch
> 0004-x86-kdump-move-reserve_crashkernel-_low-into-crash_c.patch
> 0005-arm64-kdump-introduce-some-macroes-for-crash-kernel-.patch
> 0006-arm64-kdump-reimplement-crashkernel-X.patch
> 0007-arm64-kdump-add-memory-for-devices-by-DT-property-li.patch
> 0008-kdump-update-Documentation-about-crashkernel.patch
> 
> 0001-0003 are some x86 cleanups which prepares for making
> functionsreserve_crashkernel[_low]() generic.
> 0004 makes functions reserve_crashkernel[_low]() generic.
> 0005-0006 reimplements arm64 crashkernel=X.
> 0007 adds memory for devices by DT property linux,usable-memory-range.
> 0008 updates the doc.
> 
> Changes since [v12]
> - Rebased on top of 5.10-rc1.
> - Keep CRASH_ALIGN as 16M suggested by Dave.
> - Drop patch "kdump: add threshold for the required memory".
> - Add Tested-by from John.
> 
> Changes since [v11]
> - Rebased on top of 5.9-rc4.
> - Make the function reserve_crashkernel() of x86 generic.
> Suggested by Catalin, make the function reserve_crashkernel() of x86 generic
> and arm64 use the generic version to reimplement crashkernel=X.
> 
> Changes since [v10]
> - Reimplement crashkernel=X suggested by Catalin, Many thanks to Catalin.
> 
> Changes since [v9]
> - Patch 1 add Acked-by from Dave.
> - Update patch 5 according to Dave's comments.
> - Update chosen schema.
> 
> Changes since [v8]
> - Reuse DT property "linux,usable-memory-range".
> Suggested by Rob, reuse DT property "linux,usable-memory-range" to pass the low
> memory region.
> - Fix kdump broken with ZONE_DMA reintroduced.
> - Update chosen schema.
> 
> Changes since [v7]
> - Move x86 CRASH_ALIGN to 2M
> Suggested by Dave and do some test, move x86 CRASH_ALIGN to 2M.
> - Update Documentation/devicetree/bindings/chosen.txt.
> Add corresponding documentation to Documentation/devicetree/bindings/chosen.txt
> suggested by Arnd.
> - Add Tested-by from Jhon and pk.
> 
> Changes since [v6]
> - Fix build errors reported by kbuild test robot.
> 
> Changes since [v5]
> - Move reserve_crashkernel_low() into kernel/crash_core.c.
> - Delete crashkernel=X,high.
> - Modify crashkernel=X,low.
> If crashkernel=X,low is specified simultaneously, reserve spcified size low
> memory for crash kdump kernel devices firstly and then reserve memory above 4G.
> In addition, rename crashk_low_res as "Crash kernel (low)" for arm64, and then
> pass to crash dump kernel by DT property "linux,low-memory-range".
> - Update Documentation/admin-guide/kdump/kdump.rst.
> 
> Changes since [v4]
> - Reimplement memblock_cap_memory_ranges for multiple ranges by Mike.
> 
> Changes since [v3]
> - Add memblock_cap_memory_ranges back for multiple ranges.
> - Fix some compiling warnings.
> 
> Changes since [v2]
> - Split patch "arm64: kdump: support reserving crashkernel above 4G" as
> two. Put "move reserve_crashkernel_low() into kexec_core.c" in a separate
> patch.
> 
> Changes since [v1]:
> - Move common reserve_crashkernel_low() code into kernel/kexec_core.c.
> - Remove memblock_cap_memory_ranges() i added in v1 and implement that
> in fdt_enforce_memory_region().
> There are at most two crash kernel regions, for two crash kernel regions
> case, we cap the memory range [min(regs[*].start), max(regs[*].end)]
> and then remove the memory range in the middle.
> 
> [1]: http://lists.infradead.org/pipermail/kexec/2020-June/020737.html
> [2]: https://github.com/robherring/dt-schema/pull/19 
> [v1]: https://lkml.org/lkml/2019/4/2/1174
> [v2]: https://lkml.org/lkml/2019/4/9/86
> [v3]: https://lkml.org/lkml/2019/4/9/306
> [v4]: https://lkml.org/lkml/2019/4/15/273
> [v5]: https://lkml.org/lkml/2019/5/6/1360
> [v6]: https://lkml.org/lkml/2019/8/30/142
> [v7]: https://lkml.org/lkml/2019/12/23/411
> [v8]: https://lkml.org/lkml/2020/5/21/213
> [v9]: https://lkml.org/lkml/2020/6/28/73
> [v10]: https://lkml.org/lkml/2020/7/2/1443
> [v11]: https://lkml.org/lkml/2020/8/1/150
> [v12]: https://lkml.org/lkml/2020/9/7/1037
> 
> Chen Zhou (8):
>   x86: kdump: replace the hard-coded alignment with macro CRASH_ALIGN
>   x86: kdump: make the lower bound of crash kernel reservation
>     consistent
>   x86: kdump: use macro CRASH_ADDR_LOW_MAX in functions
>     reserve_crashkernel()
>   x86: kdump: move reserve_crashkernel[_low]() into crash_core.c
>   arm64: kdump: introduce some macroes for crash kernel reservation
>   arm64: kdump: reimplement crashkernel=X
>   arm64: kdump: add memory for devices by DT property
>     linux,usable-memory-range
>   kdump: update Documentation about crashkernel
> 
>  Documentation/admin-guide/kdump/kdump.rst     |  23 ++-
>  .../admin-guide/kernel-parameters.txt         |  12 +-
>  arch/arm64/include/asm/kexec.h                |  15 ++
>  arch/arm64/include/asm/processor.h            |   1 +
>  arch/arm64/kernel/setup.c                     |  13 +-
>  arch/arm64/mm/init.c                          | 105 ++++-------
>  arch/arm64/mm/mmu.c                           |   4 +
>  arch/x86/include/asm/kexec.h                  |  28 +++
>  arch/x86/kernel/setup.c                       | 153 +---------------
>  include/linux/crash_core.h                    |   4 +
>  include/linux/kexec.h                         |   2 -
>  kernel/crash_core.c                           | 168 ++++++++++++++++++
>  kernel/kexec_core.c                           |  17 --
>  13 files changed, 301 insertions(+), 244 deletions(-)
> 
> -- 
> 2.20.1
> 

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