Re: [PATCH v22 0/9] support reserving crashkernel above 4G on arm64 kdump

From: Leizhen (ThunderTown)
Date: Sun Apr 24 2022 - 22:19:55 EST

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Hi, Catalin Marinas and Will Deacon:
Do you have time to review patches 3-4 and 6-7? These patches are a little more
relevant to the arm64 architecture.

Hi, Baoquan He:
Can you review patches 1 and 5 again?

On 2022/4/14 19:57, Zhen Lei wrote:
> Changes since [v21]:
> 1. Update the commit message of patch 1 and 5.
> 2. Add some comments for reserve_crashkernel() in patch 5.
>
> Thanks to Baoquan He and John Donnelly for their review comments.
>
> Because v5.18-rc1 has added a new patch
> commit 031495635b46 ("arm64: Do not defer reserve_crashkernel() for platforms with no DMA memory zones")
> There are many new scenarios:
> 1) The mappings may be block or page-level.
> 2) The call to reserve_crashkernel() may or may not be deferred.
> 3) The the upper limit of DMA address may be 4G, or less than 4G. Or the
> upper limit of physical memory, because SMMU can do the mapping.
>
> The code of patch 1-2, 8-9 keep no change, because the above-mentioned issues are not involved.
> The code of patch 5 only makes the following changes:
> - if (crash_base >= SZ_4G)
> + /*
> + * When both CONFIG_ZONE_DMA and CONFIG_ZONE_DMA32 are disabled, the
> + * CRASH_ADDR_LOW_MAX equals the upper limit of physical memory, so
> + * the 'crash_base' of high memory can not exceed it. To follow the
> + * description of "crashkernel=X,high" option, add below 'high'
> + * condition to make sure the crash low memory will be reserved.
> + */
> + if ((crash_base >= CRASH_ADDR_LOW_MAX) || high) {
> Change SZ_4G to CRASH_ADDR_LOW_MAX, because arm64_dma_phys_limit may be less than
> 4G or greater than 4G. The check 'high' is used for "crashkernel=X,high" and
> "(crash_base >= CRASH_ADDR_LOW_MAX)" is used for "crashkernel=X[@offset]".
>
> Patch 3-4 to allow block mappings for memory above 4G.
> Patch 6-7 to support only crash high memory or fixed memory range specified by
> crashkernel=X@offset use page-level mapping, to allow other areas use block mapping.
> These four patches are for performance optimization purposes. For details about the
> technical feasibility analysis, please see the commit messages.
>
> Now the implementation of arm64 is very different from that of x86. It's no longer
> suitable for both of them to share code.
>
>
>
> Changes since [v20]:
> 1. Check whether crashkernel=Y,low is incorrectly configured or not configured. Do different processing.
> 2. Share the existing description of x86. The configuration of arm64 is the same as that of x86.
> 3. Define the value of macro CRASH_ADDR_HIGH_MAX as memblock.current_limit, instead of MEMBLOCK_ALLOC_ACCESSIBLE.
> 4. To improve readability, some lightweight code adjustments have been made to reserve_craskernel(), including comments.
> 5. The defined value of DEFAULT_CRASH_KERNEL_LOW_SIZE reconsiders swiotlb, just like x86, to share documents.
>
> Thanks to Baoquan He for his careful review.
>
> The test cases are as follows: (Please update the kexec tool to the latest version)
> 1) crashkernel=4G //high=4G, low=256M
> 2) crashkernel=4G crashkernel=512M,high crashkernel=512M,low //high=4G, low=256M, high and low are ignored
> 3) crashkernel=4G crashkernel=512M,high //high=4G, low=256M, high is ignored
> 4) crashkernel=4G crashkernel=512M,low //high=4G, low=256M, low is ignored
> 5) crashkernel=4G@0xe0000000 //high=0G, low=0M, cannot allocate, failed
> 6) crashkernel=512M //high=0G, low=512M
> 7) crashkernel=128M //high=0G, low=128M
> 8) crashkernel=512M@0xde000000 //512M@3552M //high=0G, low=512M
> 9) crashkernel=4G,high //high=4G, low=256M
> a) crashkernel=4G,high crashkernel=512M,low //high=4G, low=512M
> b) crashkernel=512M,high crashkernel=128M,low //high=512M, low=128M
> c) crashkernel=128M,high //high=128M, low=256M
> d) crashkernel=512M,low //high=0G, low=0M, invalid
> e) crashkernel=512M,high crashkernel=0,low //high=512M, low=0M
> f) crashkernel=4G,high crashkernel=ab,low //high=0G, low=0M, invalid
>
>
> 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@xxxxxxxxxx>" for patch 1-9
> - Add "Reviewed-by: Rob Herring <robh@xxxxxxxxxx>" 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.
>
> v1:
> 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])
>
>
> [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
> [v20]: https://lkml.org/lkml/2022/1/24/167
> [v21]: https://lkml.org/lkml/2022/2/26/350
>
> Chen Zhou (2):
> arm64: kdump: Reimplement crashkernel=X
> of: fdt: Add memory for devices by DT property
> "linux,usable-memory-range"
>
> Zhen Lei (7):
> kdump: return -ENOENT if required cmdline option does not exist
> arm64: Use insert_resource() to simplify code
> arm64: kdump: Remove some redundant checks in map_mem()
> arm64: kdump: Don't force page-level mappings for memory above 4G
> arm64: kdump: Use page-level mapping for the high memory of
> crashkernel
> arm64: kdump: Try not to use NO_BLOCK_MAPPINGS for memory under 4G
> docs: kdump: Update the crashkernel description for arm64
>
> .../admin-guide/kernel-parameters.txt | 8 +-
> arch/arm64/include/asm/kexec.h | 2 +
> 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 | 204 +++++++++++++++++-
> arch/arm64/mm/mmu.c | 68 +++---
> drivers/of/fdt.c | 33 ++-
> kernel/crash_core.c | 3 +-
> 9 files changed, 278 insertions(+), 78 deletions(-)
>

--
Regards,
Zhen Lei

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