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c450c8f532
The current implementation of in_exception_stack() iterates over the exception stacks array. Most of the time this is an useless exercise, but even for the actual use cases (perf and ftrace) it takes at least 2 iterations to get to the NMI stack. As the exception stacks and the guard pages are page aligned the loop can be avoided completely. Add a initial check whether the stack pointer is inside the full exception stack area and leave early if not. Create a lookup table which describes the stack area. The table index is the page offset from the beginning of the exception stacks. So for any given stack pointer the page offset is computed and a lookup in the description table is performed. If it is inside a guard page, return. If not, use the descriptor to fill in the info structure. The table is filled at compile time and for the !KASAN case the interesting page descriptors exactly fit into a single cache line. Just the last guard page descriptor is in the next cacheline, but that should not be accessed in the regular case. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Borislav Petkov <bp@suse.de> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Sean Christopherson <sean.j.christopherson@intel.com> Cc: x86-ml <x86@kernel.org> Link: https://lkml.kernel.org/r/20190414160145.543320386@linutronix.de |
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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.