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Some drivers want to use cpu_logical_map(), early_cpu_to_node() and some other CPU mapping APIs, even if we use "nr_cpus=1" to hard limit the CPU number. This is strongly required for the multi-bridges machines. Currently, we stop parsing the MADT if the nr_cpus limit is reached, but to achieve the above goal we should always enumerate the MADT table and setup logical-physical CPU mapping whether there is a nr_cpus limit. Rework the MADT enumeration: 1. Define a flag "cpu_enumerated" to distinguish the first enumeration (cpu_enumerated=0) and the physical hotplug case (cpu_enumerated=1) for set_processor_mask(). 2. If cpu_enumerated=0, stop parsing only when NR_CPUS limit is reached, so we can setup logical-physical CPU mapping; if cpu_enumerated=1, stop parsing when nr_cpu_ids limit is reached, so we can avoid some runtime bugs. Once logical-physical CPU mapping is setup, we will let cpu_enumerated=1. 3. Use find_first_zero_bit() instead of cpumask_next_zero() to find the next zero bit (free logical CPU id) in the cpu_present_mask, because cpumask_next_zero() will stop at nr_cpu_ids. 4. Only touch cpu_possible_mask if cpu_enumerated=0, this is in order to avoid some potential crashes, because cpu_possible_mask is marked as __ro_after_init. 5. In prefill_possible_map(), clear cpu_present_mask bits greater than nr_cpu_ids, in order to avoid a CPU be "present" but not "possible". Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
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 reStructuredText 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.