mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-04-29 04:41:21 -04:00
4f6b64f3d3
Current code gets the APIC IDs for CPUs numbered 255 and lower. This code assumes cpu_possible_mask is dense, which is not true in the general case per [1]. If cpu_possible_mask contains holes, num_possible_cpus() is less than nr_cpu_ids, so some CPUs might get skipped. Furthermore, getting the APIC ID of a CPU that isn't in cpu_possible_mask is invalid. However, the configurations that Hyper-V provides to guest VMs on x86 hardware, in combination with how x86 code assigns Linux CPU numbers, *does* always produce a dense cpu_possible_mask. So the dense assumption is not currently causing failures. But for robustness against future changes in how cpu_possible_mask is populated, update the code to no longer assume dense. The correct approach is to determine the range to scan based on nr_cpu_ids, and skip any CPUs that are not in the cpu_possible_mask. [1] https://lore.kernel.org/lkml/SN6PR02MB4157210CC36B2593F8572E5ED4692@SN6PR02MB4157.namprd02.prod.outlook.com/ Signed-off-by: Michael Kelley <mhklinux@outlook.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20241003035333.49261-4-mhklinux@outlook.com Signed-off-by: Wei Liu <wei.liu@kernel.org> Message-ID: <20241003035333.49261-4-mhklinux@outlook.com>
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.