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If nr_cpu_ids is too low to include the boot CPU, remap the boot CPU onto logical core 0. This is achieved in two stages. In early_init_dt_scan_cpus() the boot CPU is renumbered to be on logical core 0, and the original boot core's hardware ID is recorded. Later in smp_setup_cpu_maps(), if the original boot core ID is set, the logical CPU numbers on the 0th core are skipped in the normal device tree search over CPU device tree nodes. Then the search is continued until the device tree node matching the boot core is found, and those CPUs are assigned the CPU numbers starting at 0. This allows kdump kernels to be booted with low values for nr_cpu_ids to conserve memory, while also allowing the crashing/boot CPU to be any CPU. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Tested-by: Wen Xiong <wenxiong@us.ibm.com> Link: https://msgid.link/20231229120107.2281153-5-mpe@ellerman.id.au
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.