Documentation: dt: chosen properties for arm64 kdump
Add documentation for
linux,crashkernel-base and crashkernel-size,
linux,usable-memory-range
linux,elfcorehdr
used by arm64 kdump to decribe the kdump reserved area, and
the elfcorehdr's location within it.
Signed-off-by: James Morse <email address hidden>
[<email address hidden>: added "linux,crashkernel-base" and "-size" ]
Signed-off-by: AKASHI Takahiro <email address hidden>
Cc: <email address hidden>
Cc: Rob Herring <email address hidden>
Cc: Mark Rutland <email address hidden>
[v29 submittal]
Add arch-specific functions to provide a dump file, /proc/vmcore.
This file is in ELF format and its ELF header needs to be prepared by
userspace tools, like kexec-tools, in adance. The primary kernel is
responsible to allocate the region with reserve_elfcorehdr() at boot time
and advertize its location to crash dump kernel via a new device-tree
property, "linux,elfcorehdr".
Then crash dump kernel will access the primary kernel's memory with
copy_oldmem_page(), which feeds the data page-by-page by ioremap'ing it
since it does not reside in linear mapping on crash dump kernel.
We also need our own elfcorehdr_read() here since the header is placed
within crash dump kernel's usable memory.
arm64: kdump: add VMCOREINFO's for user-space tools
In addition to common VMCOREINFO's defined in
crash_save_vmcoreinfo_init(), we need to know, for crash utility,
- kimage_voffset
- PHYS_OFFSET
to examine the contents of a dump file (/proc/vmcore) correctly
due to the introduction of KASLR (CONFIG_RANDOMIZE_BASE) in v4.6.
- VA_BITS
is also required for makedumpfile command.
arch_crash_save_vmcoreinfo() appends them to the dump file.
More VMCOREINFO's may be added later.
Primary kernel calls machine_crash_shutdown() to shut down non-boot cpus
and save registers' status in per-cpu ELF notes before starting crash
dump kernel. See kernel_kexec().
Even if not all secondary cpus have shut down, we do kdump anyway.
As we don't have to make non-boot(crashed) cpus offline (to preserve
correct status of cpus at crash dump) before shutting down, this patch
also adds a variant of smp_send_stop().
arm64: kdump: reserve memory for crash dump kernel
"crashkernel=" kernel parameter specifies the size (and optionally
the start address) of the system ram used by crash dump kernel.
reserve_crashkernel() will allocate and reserve the memory at the startup
of primary kernel.
This memory range will be exported to userspace via:
- an entry named "Crash kernel" in /proc/iomem, and
- "linux,crashkernel-base" and "linux,crashkernel-size" under
/sys/firmware/devicetree/base/chosen
arm64: limit memory regions based on DT property, usable-memory-range
Crash dump kernel utilizes only a subset of available memory as System RAM.
On arm64 kdump, This memory range is advertized to crash dump kernel via
a device-tree property under /chosen,
linux,usable-memory-range = <BASE SIZE>
Crash dump kernel reads this property at boot time and calls
memblock_cap_memory_range() to limit usable memory ranges which are
described as entries in UEFI memory map table or "memory" nodes in
a device tree blob.
Add memblock_cap_memory_range() which will remove all the memblock regions
except the memory range specified in the arguments. In addition, rework is
done on memblock_mem_limit_remove_map() to re-implement it using
memblock_cap_memory_range().
This function, like memblock_mem_limit_remove_map(), will not remove
memblocks with MEMMAP_NOMAP attribute as they may be mapped and accessed
later as "device memory."
See the commit a571d4eb55d8 ("mm/memblock.c: add new infrastructure to
address the mem limit issue").
This function is used, in a succeeding patch in the series of arm64 kdump
suuport, to limit the range of usable memory, or System RAM, on crash dump
kernel.
(Please note that "mem=" parameter is of little use for this purpose.)
