Date:   Tue, 30 Nov 2021 10:12:01 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Zhen Lei <thunder.leizhen@huawei.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
        linux-kernel@vger.kernel.org, Dave Young <dyoung@redhat.com>,
        Vivek Goyal <vgoyal@redhat.com>,
        Eric Biederman <ebiederm@xmission.com>,
        kexec@lists.infradead.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        devicetree@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
        linux-doc@vger.kernel.org, Randy Dunlap <rdunlap@infradead.org>,
        Feng Zhou <zhoufeng.zf@bytedance.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Chen Zhou <dingguo.cz@antgroup.com>
Subject: Re: [PATCH v16 00/11] support reserving crashkernel above 4G on
 arm64 kdump
Message-ID: <20211130021201.GM21646@MiWiFi-R3L-srv>
References: <20211123124646.1995-1-thunder.leizhen@huawei.com>
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Hi Lei,

On 11/23/21 at 08:46pm, Zhen Lei 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.
> 
> To solve these issues, change the behavior of crashkernel=X.
> crashkernel=X tries low allocation in DMA zone and fall back to high
> allocation if it fails.

Thanks for this round of posting, I will review the patch series this
week.

Thanks
Baoquan

> 
> 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 and "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 11 patches:
> 
> 0001-0004 are some x86 cleanups which prepares for making functionsreserve_crashkernel[_low]() generic.
> 0005 makes functions reserve_crashkernel[_low]() generic.
> 0006-0008 reimplements arm64 crashkernel=X.
> 0009-0010 adds memory for devices by DT property linux,usable-memory-range.
> 0011 updates the doc.
> 
> Changes since [v15]
> -  Aggregate the processing of "linux,usable-memory-range" into one function.
>    Only patch 9-10 have been updated.
> 
> Changes since [v14]
> - Recovering the requirement that the CrashKernel memory regions on X86
>   only requires 1 MiB alignment.
> - Combine patches 5 and 6 in v14 into one. The compilation warning fixed
>   by patch 6 was introduced by patch 5 in v14.
> - As with crashk_res, crashk_low_res is also processed by
>   crash_exclude_mem_range() in patch 7.
> - Due to commit b261dba2fdb2 ("arm64: kdump: Remove custom linux,usable-memory-range handling")
>   has removed the architecture-specific code, extend the property "linux,usable-memory-range"
>   in the platform-agnostic FDT core code. See patch 9.
> - Discard the x86 description update in the document, because the description
>   has been updated by commit b1f4c363666c ("Documentation: kdump: update kdump guide").
> - Change "arm64" to "ARM64" in Doc.
> 
> 
> Changes since [v13]
> - Rebased on top of 5.11-rc5.
> - Introduce config CONFIG_ARCH_WANT_RESERVE_CRASH_KERNEL.
> Since reserve_crashkernel[_low]() implementations are quite similar on
> other architectures, so have CONFIG_ARCH_WANT_RESERVE_CRASH_KERNEL in
> arch/Kconfig and select this by X86 and ARM64.
> - Some minor cleanup.
> 
> 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
> [v13]: https://lkml.org/lkml/2020/10/31/34
> [v14]: https://lkml.org/lkml/2021/1/30/53
> [v15]: https://lkml.org/lkml/2021/10/19/1405
> 
> Chen Zhou (10):
>   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 xen_pv_domain() check and insert_resource() to
>     setup_arch()
>   x86: kdump: move reserve_crashkernel[_low]() into crash_core.c
>   arm64: kdump: introduce some macros for crash kernel reservation
>   arm64: kdump: reimplement crashkernel=X
>   x86, arm64: Add ARCH_WANT_RESERVE_CRASH_KERNEL config
>   of: fdt: Add memory for devices by DT property
>     "linux,usable-memory-range"
>   kdump: update Documentation about crashkernel
> 
> Zhen Lei (1):
>   of: fdt: Aggregate the processing of "linux,usable-memory-range"
> 
>  Documentation/admin-guide/kdump/kdump.rst     |  11 +-
>  .../admin-guide/kernel-parameters.txt         |  11 +-
>  arch/Kconfig                                  |   3 +
>  arch/arm64/Kconfig                            |   1 +
>  arch/arm64/include/asm/kexec.h                |  10 ++
>  arch/arm64/kernel/machine_kexec_file.c        |  12 +-
>  arch/arm64/kernel/setup.c                     |  13 +-
>  arch/arm64/mm/init.c                          |  59 ++-----
>  arch/x86/Kconfig                              |   2 +
>  arch/x86/include/asm/elf.h                    |   3 +
>  arch/x86/include/asm/kexec.h                  |  31 +++-
>  arch/x86/kernel/setup.c                       | 163 ++----------------
>  drivers/of/fdt.c                              |  45 +++--
>  include/linux/crash_core.h                    |   3 +
>  include/linux/kexec.h                         |   2 -
>  kernel/crash_core.c                           | 156 +++++++++++++++++
>  kernel/kexec_core.c                           |  17 --
>  17 files changed, 304 insertions(+), 238 deletions(-)
> 
> -- 
> 2.25.1
>