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For the "nosmp" use case, the APIC initialization code selects "APIC_SYMMETRIC_IO_NO_ROUTING" as the default interrupt mode and avoids probing APIC drivers. This works well for the default APIC modes, but for the x2APIC case the probe function is required to allocate the cluster_hotplug mask. So in the APIC_SYMMETRIC_IO_NO_ROUTING case when the x2APIC is initialized it dereferences a NULL pointer and the kernel crashes. This was observed on a TDX platform where x2APIC is enabled and "nosmp" command line option is allowed. To fix this issue, probe APIC drivers via default_setup_apic_routing() for the APIC_SYMMETRIC_IO_NO_ROUTING interrupt mode too. Suggested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Tony Luck <tony.luck@intel.com> Link: https://lore.kernel.org/r/a64f864e1114bcd63593286aaf61142cfce384ea.1650076869.git.sathyanarayanan.kuppuswamy@intel.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 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.