Date:   Mon, 7 Feb 2022 12:04:48 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        <x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>,
        <linux-kernel@...r.kernel.org>, Dave Young <dyoung@...hat.com>,
        Baoquan He <bhe@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        <kexec@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Will Deacon" <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        <devicetree@...r.kernel.org>, Jonathan Corbet <corbet@....net>,
        <linux-doc@...r.kernel.org>
CC:     Randy Dunlap <rdunlap@...radead.org>,
        Feng Zhou <zhoufeng.zf@...edance.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        "Chen Zhou" <dingguo.cz@...group.com>,
        John Donnelly <John.p.donnelly@...cle.com>,
        Dave Kleikamp <dave.kleikamp@...cle.com>
Subject: Re: [PATCH v20 0/5] support reserving crashkernel above 4G on arm64
 kdump

Hi everybody:
  Can someone take a moment to review these patches? Maybe I should just try
making generic. This patch series seems to have gone back to square one,
discarding some of the valuable comments that were made in the middle. But the
only benefit of make generic is to avoid code duplication, a lot of adaptation
is needed. I think Borislav Petkov's suggestion is good, too.

  These patches are taking too long. Maybe no one wants to look through history
anymore. So I'm putting together some of the most central observations of
"make generic" as follows:
   Mike Rapoport:
     This very reminds what x86 does. Any chance some of the code can be reused
     rather than duplicated?
     https://lkml.org/lkml/2019/4/4/1225

     I think it would be better to have CONFIG_ARCH_WANT_RESERVE_CRASH_KERNEL
     in arch/Kconfig and select this by X86 and ARM64.
     https://lkml.org/lkml/2020/11/12/224

   Ingo Molnar:
     No objections for this to be merged via the ARM tree, as long as x86
     functionality is kept intact.
     https://lkml.org/lkml/2019/4/10/109

     I.e. Ack, but only if it doesn't break anything. :-)
     https://lkml.org/lkml/2019/4/12/66

   Dave Young:
     Other than the comments from James, can you move the function into
     kernel/crash_core.c, we already have some functions moved there for
     sharing.
     https://lkml.org/lkml/2019/6/12/248

   Catalin Marinas:
     Except for the threshold to keep zone ZONE_DMA memory,
     reserve_crashkernel() looks very close to the x86 version. Shall we try
     to make this generic as well?
     https://lkml.org/lkml/2020/9/2/917

   Borislav Petkov:
     Why insert_resource() is relevant only to x86?
     --> I think this means "Why does arm64 not use insert_resource()?"
     https://lkml.org/lkml/2021/12/23/480

     This is exactly why I say that making those functions generic and shared
     might not be such a good idea, after all, because then you'd have to
     sprinkle around arch-specific stuff.
     https://lkml.org/lkml/2021/12/23/480

     What I suggested and what would be real clean is if the arches would
     simply call a *single*
	parse_crashkernel()
     function and when that one returns, *all* crashkernel= options would
     have been parsed properly, low, high, middle crashkernel, whatever...
     and the caller would know what crash kernel needs to be allocated.
     https://lkml.org/lkml/2021/12/28/305

   ------
   James Morse:
     We can then describe it via a different string in /proc/iomem, something
     like "Crash kernel (low)".
     https://lkml.org/lkml/2019/6/5/670
     --> The suggestion looks out of date. See Borislav Petkov's comments:
     --> 157752d84f5d ("kexec: use Crash kernel for Crash kernel low")
     --> https://lkml.org/lkml/2021/12/23/480


On 2022/1/24 16:47, 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.
> 
> 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])
> 
> 
> Changes since [v19]:
> 1. Temporarily stop making reserve_crashkernel[_low]() generic. There are a
>    lot of details need to be considered, which can take a long time. Because
>    "make generic" does not add new functions and does not improve performance,
>    maybe I should say it's just a cleanup. So by stripping it out and leaving
>    it for other patches later, we can aggregate the changes to the main functions.
> 2. Use insert_resource() to replace request_resource(), this not only simplifies
>    the code, but also reduces the differences between arm64 and x86 implementations.
> 3. As commit 157752d84f5d ("kexec: use Crash kernel for Crash kernel low") do for
>    x86, we can also extend kexec-tools for arm64, and it's currently applied. See:
>    https://www.spinics.net/lists/kexec/msg28284.html
> 
> Thank you very much, Borislav Petkov, for so many valuable comments.
> 
> 
> 
> Changes since [v17]: v17 --> v19
> 1. Patch 0001-0004
>    Introduce generic parse_crashkernel_high_low() to bring the parsing of
>    "crashkernel=X,high" and the parsing of "crashkernel=X,low" together,
>    then use it instead of the call to parse_crashkernel_{high|low}(). Two
>    confusing parameters of parse_crashkernel_{high|low}() are deleted.
> 
>    I previously sent these four patches separately:
>    [1] https://lkml.org/lkml/2021/12/25/40
> 2. Patch 0005-0009
>    Introduce generic reserve_crashkernel_mem[_low](), the implementation of
>    these two functions is based on function reserve_crashkernel[_low]() in
>    arch/x86/kernel/setup.c. There is no functional change for x86.
>    1) The check position of xen_pv_domain() does not change.
>    2) Still 1M alignment for crash kernel fixed region, when 'base' is specified.
> 
>    To avoid compilation problems on other architectures: patch 0004 moves
>    the definition of global variable crashk[_low]_res from kexec_core.c to
>    crash_core.c, and provide default definitions for all macros involved, a
>    particular platform can redefine these macros to override the default
>    values.
> 3. 0010, only one line of comment was changed.
> 4. 0011
>    1) crashk_low_res may also a valid reserved memory, should be checked
>       in crash_is_nosave(), see arch/arm64/kernel/machine_kexec.
>    2) Drop memblock_mark_nomap() for crashk_low_res, because of:
>       2687275a5843 arm64: Force NO_BLOCK_MAPPINGS if crashkernel reservation is required
>    3) Also call kmemleak_ignore_phys() for crashk_low_res, because of:
>       85f58eb18898 arm64: kdump: Skip kmemleak scan reserved memory for kdump
> 5. 0012, slightly rebased, because the following patch is applied in advance. 
>    https://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git/commit/?h=dt/linus&id=8347b41748c3019157312fbe7f8a6792ae396eb7
> 6. 0013, no change.
> 
> Others:
> 1. Discard add ARCH_WANT_RESERVE_CRASH_KERNEL
> 2. When allocating crash low memory, the start address still starts from 0.
>    low_base = memblock_phys_alloc_range(low_size, CRASH_ALIGN, 0, CRASH_ADDR_LOW_MAX);
> 3. Discard change (1ULL << 32) to CRASH_ADDR_LOW_MAX.
> 4. Ensure the check position of xen_pv_domain() have no change.
> 5. Except patch 0010 and 0012, all "Tested-by", "Reviewed-by", "Acked-by" are removed.
> 6. Update description.
> 
> 
> 
> Changes since [v16]
> - Because no functional changes in this version, so add
>   "Tested-by: Dave Kleikamp <dave.kleikamp@...cle.com>" for patch 1-9
> - Add "Reviewed-by: Rob Herring <robh@...nel.org>" for patch 8
> - Update patch 9 based on the review comments of Rob Herring
> - As Catalin Marinas's suggestion, merge the implementation of
>   ARCH_WANT_RESERVE_CRASH_KERNEL into patch 5. Ensure that the
>   contents of X86 and ARM64 do not overlap, and reduce unnecessary
>   temporary differences.
> 
> 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]: https://www.spinics.net/lists/kexec/msg28226.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
> [v16]: https://lkml.org/lkml/2021/11/23/435
> [v17]: https://lkml.org/lkml/2021/12/10/38
> [v18]: https://lkml.org/lkml/2021/12/22/424
> [v19]: https://lkml.org/lkml/2021/12/28/203
> 
> 
> Chen Zhou (4):
>   arm64: kdump: introduce some macros for crash kernel reservation
>   arm64: kdump: reimplement crashkernel=X
>   of: fdt: Add memory for devices by DT property
>     "linux,usable-memory-range"
>   kdump: update Documentation about crashkernel
> 
> Zhen Lei (1):
>   arm64: Use insert_resource() to simplify code
> 
>  Documentation/admin-guide/kdump/kdump.rst     | 11 ++-
>  .../admin-guide/kernel-parameters.txt         | 11 ++-
>  arch/arm64/kernel/machine_kexec.c             |  9 ++-
>  arch/arm64/kernel/machine_kexec_file.c        | 12 ++-
>  arch/arm64/kernel/setup.c                     | 17 +---
>  arch/arm64/mm/init.c                          | 80 +++++++++++++++++--
>  drivers/of/fdt.c                              | 33 +++++---
>  7 files changed, 134 insertions(+), 39 deletions(-)
> 

-- 
Regards,
  Zhen Lei

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