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Subject[PATCH v17 00/10] support reserving crashkernel above 4G on arm64 kdump
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])

This patchset contains the following 10 patches:

0001-0004 are some x86 cleanups which prepares for making functionsreserve_crashkernel[_low]() generic.
0005 makes functions reserve_crashkernel[_low]() generic.
0006-0007 reimplements arm64 crashkernel=X.
0008-0009 adds memory for devices by DT property linux,usable-memory-range.
0010 updates the doc.

Changes since [v16]
- Because no functional changes in this version, so add
"Tested-by: Dave Kleikamp <>" for patch 1-9
- Add "Reviewed-by: Rob Herring <>" 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.
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

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.


Chen Zhou (9):
x86: kdump: replace the hard-coded alignment with macro CRASH_ALIGN
x86: kdump: make the lower bound of crash kernel reservation
x86: kdump: use macro CRASH_ADDR_LOW_MAX in functions
x86: kdump: move xen_pv_domain() check and insert_resource() to
x86: kdump: move reserve_crashkernel[_low]() into crash_core.c
arm64: kdump: introduce some macros for crash kernel reservation
arm64: kdump: reimplement crashkernel=X
of: fdt: Add memory for devices by DT property
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 | 42 +++--
include/linux/crash_core.h | 3 +
include/linux/kexec.h | 2 -
kernel/crash_core.c | 156 +++++++++++++++++
kernel/kexec_core.c | 17 --
17 files changed, 301 insertions(+), 238 deletions(-)


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