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c0213b0ac0
Currently, the patch of an address is done in three steps: -- Pseudo-code #1 - Current implementation --- 1) add an int3 trap to the address that will be patched sync cores (send IPI to all other CPUs) 2) update all but the first byte of the patched range sync cores (send IPI to all other CPUs) 3) replace the first byte (int3) by the first byte of replacing opcode sync cores (send IPI to all other CPUs) -- Pseudo-code #1 --- When a static key has more than one entry, these steps are called once for each entry. The number of IPIs then is linear with regard to the number 'n' of entries of a key: O(n*3), which is O(n). This algorithm works fine for the update of a single key. But we think it is possible to optimize the case in which a static key has more than one entry. For instance, the sched_schedstats jump label has 56 entries in my (updated) fedora kernel, resulting in 168 IPIs for each CPU in which the thread that is enabling the key is _not_ running. With this patch, rather than receiving a single patch to be processed, a vector of patches is passed, enabling the rewrite of the pseudo-code #1 in this way: -- Pseudo-code #2 - This patch --- 1) for each patch in the vector: add an int3 trap to the address that will be patched sync cores (send IPI to all other CPUs) 2) for each patch in the vector: update all but the first byte of the patched range sync cores (send IPI to all other CPUs) 3) for each patch in the vector: replace the first byte (int3) by the first byte of replacing opcode sync cores (send IPI to all other CPUs) -- Pseudo-code #2 - This patch --- Doing the update in this way, the number of IPI becomes O(3) with regard to the number of keys, which is O(1). The batch mode is done with the function text_poke_bp_batch(), that receives two arguments: a vector of "struct text_to_poke", and the number of entries in the vector. The vector must be sorted by the addr field of the text_to_poke structure, enabling the binary search of a handler in the poke_int3_handler function (a fast path). Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Chris von Recklinghausen <crecklin@redhat.com> Cc: Clark Williams <williams@redhat.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Jason Baron <jbaron@akamai.com> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Scott Wood <swood@redhat.com> Cc: Steven Rostedt (VMware) <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/ca506ed52584c80f64de23f6f55ca288e5d079de.1560325897.git.bristot@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
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| net | ||
| samples | ||
| scripts | ||
| security | ||
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| tools | ||
| usr | ||
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| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
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| Kbuild | ||
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| 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.