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Subject: Re: [PATCH v13 0/8] support reserving crashkernel above 4G on arm64
 kdump
To:     Baoquan He <bhe@redhat.com>, <bhsharma@redhat.com>
References: <20201031074437.168008-1-chenzhou10@huawei.com>
 <20201111030136.GD8486@MiWiFi-R3L-srv>
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        <horms@verge.net.au>, <robh+dt@kernel.org>, <arnd@arndb.de>,
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        <xiexiuqi@huawei.com>, <guohanjun@huawei.com>,
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From:   chenzhou <chenzhou10@huawei.com>
Message-ID: <04a893e6-1412-5fa8-8dbd-8ec278879965@huawei.com>
Date:   Wed, 11 Nov 2020 21:29:51 +0800
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Hi Baoquan, Bhupesh,


On 2020/11/11 11:01, Baoquan He wrote:
> 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.

Yeah, i also tested on x86_64 and work well. I did these basic tests before sending every
new version.
But Bhupesh may have some review comments(Bhupesh referred one month ago).

Thanks,
Chen Zhou

>
> 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
>>
> .
>