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f2d08c5d3b
The current kernel supports 5-level paging mode, and supports dynamically choosing the paging mode during bootup depending on the kernel image, hardware and kernel parameter settings. This flexibility brings several issues to kexec/kdump: 1) Dynamic switching between paging modes requires support in the target kernel. This means kexec from a 5-level paging kernel into a kernel which does not support mode switching is not possible. So the loader needs to be able to analyze the supported paging modes of the kexec target kernel. 2) If running on a 5-level paging kernel and the kexec target kernel is a 4-level paging kernel, the target immage cannot be loaded above the 64TB address space limit. But the kexec loader searches for a load area from top to bottom which would eventually put the target kernel above 64TB when the machine has large enough RAM size. So the loader needs to be able to analyze the paging mode of the target kernel to load it at a suitable spot in the address space. Solution: Add two bits XLF_5LEVEL and XLF_5LEVEL_ENABLED: - Bit XLF_5LEVEL indicates whether 5-level paging mode switching support is available. (Issue #1) - Bit XLF_5LEVEL_ENABLED indicates whether the kernel was compiled with full 5-level paging support (CONFIG_X86_5LEVEL=y). (Issue #2) The loader will use these bits to verify whether the target kernel is suitable to be kexec'ed to from a 5-level paging kernel and to determine the constraints of the target kernel load address. The flags will be used by the kernel kexec subsystem and the userspace kexec tools. [ tglx: Massaged changelog ] Signed-off-by: Baoquan He <bhe@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: bp@alien8.de Cc: hpa@zytor.com Cc: dyoung@redhat.com Link: https://lkml.kernel.org/r/20190524073810.24298-2-bhe@redhat.com |
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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.