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A bus lock is acquired through either a split locked access to writeback (WB) memory or any locked access to non-WB memory. This is typically >1000 cycles slower than an atomic operation within a cache line. It also disrupts performance on other cores. Some CPUs have the ability to notify the kernel by a #DB trap after a user instruction acquires a bus lock and is executed. This allows the kernel to enforce user application throttling or mitigation. Both breakpoint and bus lock can trigger the #DB trap in the same instruction and the ordering of handling them is the kernel #DB handler's choice. The CPU feature flag to be shown in /proc/cpuinfo will be "bus_lock_detect". Signed-off-by: Fenghua Yu <fenghua.yu@intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Tony Luck <tony.luck@intel.com> Link: https://lore.kernel.org/r/20210322135325.682257-2-fenghua.yu@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.