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A kernel that was compiled without CONFIG_X86_X2APIC was unable to boot on platforms that have x2APIC already enabled in the BIOS before starting the kernel. The kernel was supposed to panic with an approprite error message in validate_x2apic() due to the missing X2APIC support. However, validate_x2apic() was run too late in the boot cycle, and the kernel tried to initialize the APIC nonetheless. This resulted in an earlier panic in setup_local_APIC() because the APIC was not registered. In my experiments, a panic message in setup_local_APIC() was not visible in the graphical console, which resulted in a hang with no indication what has gone wrong. Instead of calling panic(), disable the APIC, which results in a somewhat working system with the PIC only (and no SMP). This way the user is able to diagnose the problem more easily. Disabling X2APIC mode is not an option because it's impossible on systems with locked x2APIC. The proper place to disable the APIC in this case is in check_x2apic(), which is called early from setup_arch(). Doing this in __apic_intr_mode_select() is too late. Make check_x2apic() unconditionally available and remove the empty stub. Reported-by: Paul Menzel <pmenzel@molgen.mpg.de> Reported-by: Robert Elliott (Servers) <elliott@hpe.com> Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/lkml/d573ba1c-0dc4-3016-712a-cc23a8a33d42@molgen.mpg.de Link: https://lore.kernel.org/lkml/20220911084711.13694-3-mat.jonczyk@o2.pl Link: https://lore.kernel.org/all/20221129215008.7247-1-mat.jonczyk@o2.pl |
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| certs | ||
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| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.