Merge branch 'next-seccomp' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security

Pull seccomp updates from James Morris:
 "Add support for retrieving seccomp metadata"

* 'next-seccomp' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security:
  ptrace, seccomp: add support for retrieving seccomp metadata
  seccomp: hoist out filter resolving logic

0 files changed, 0 insertions, 0 deletions

path: root/tools/perf/scripts/python/bin/stackcollapse-report

		CPU hotplug Support in Linux(tm) Kernel

		Maintainers:
		CPU Hotplug Core:
			Rusty Russell <rusty@rustycorp.com.au>
			Srivatsa Vaddagiri <vatsa@in.ibm.com>
		i386:
			Zwane Mwaikambo <zwane@arm.linux.org.uk>
		ppc64:
			Nathan Lynch <nathanl@austin.ibm.com>
			Joel Schopp <jschopp@austin.ibm.com>
		ia64/x86_64:
			Ashok Raj <ashok.raj@intel.com>
		s390:
			Heiko Carstens <heiko.carstens@de.ibm.com>

Authors: Ashok Raj <ashok.raj@intel.com>
Lots of feedback: Nathan Lynch <nathanl@austin.ibm.com>,
	     Joel Schopp <jschopp@austin.ibm.com>

Introduction

Modern advances in system architectures have introduced advanced error
reporting and correction capabilities in processors. CPU architectures permit
partitioning support, where compute resources of a single CPU could be made
available to virtual machine environments. There are couple OEMS that
support NUMA hardware which are hot pluggable as well, where physical
node insertion and removal require support for CPU hotplug.

Such advances require CPUs available to a kernel to be removed either for
provisioning reasons, or for RAS purposes to keep an offending CPU off
system execution path. Hence the need for CPU hotplug support in the
Linux kernel.

A more novel use of CPU-hotplug support is its use today in suspend
resume support for SMP. Dual-core and HT support makes even
a laptop run SMP kernels which didn't support these methods. SMP support
for suspend/resume is a work in progress.

General Stuff about CPU Hotplug
--------------------------------

Command Line Switches
---------------------
maxcpus=n    Restrict boot time cpus to n. Say if you have 4 cpus, using
             maxcpus=2 will only boot 2. You can choose to bring the
             other cpus later online, read FAQ's for more info.

additional_cpus=n (*)	Use this to limit hotpluggable cpus. This option sets
  			cpu_possible_map = cpu_present_map + additional_cpus

(*) Option valid only for following architectures
- x86_64, ia64

ia64 and x86_64 use the number of disabled local apics in ACPI tables MADT
to determine the number of potentially hot-pluggable cpus. The implementation
should only rely on this to count the # of cpus, but *MUST* not rely on the
apicid values in those tables for disabled apics. In the event BIOS doesn't
mark such hot-pluggable cpus as disabled entries, one could use this
parameter "additional_cpus=x" to represent those cpus in the cpu_possible_map.

possible_cpus=n		[s390 only] use this to set hotpluggable cpus.
			This option sets possible_cpus bits in
			cpu_possible_map. Thus keeping the numbers of bits set
			constant even if the machine gets rebooted.

CPU maps and such
-----------------
[More on cpumaps and primitive to manipulate, please check
include/linux/cpumask.h that has more descriptive text.]

cpu_possible_map: Bitmap of possible CPUs that can ever be available in the
system. This is used to allocate some boot time memory for per_cpu variables
that aren't designed to grow/shrink as CPUs are made available or removed.
Once set during boot time discovery phase, the map is static, i.e no bits
are added or removed anytime.  Trimming it accurately for your system needs
upfront can save some boot time memory. See below for how we use heuristics
in x86_64 case to keep this under check.

cpu_online_map: Bitmap of all CPUs currently online. Its set in __cpu_up()
after a cpu is available for kernel scheduling and ready to receive
interrupts from devices. Its cleared when a cpu is brought down using
__cpu_disable(), before which all OS services including interrupts are
migrated to another target CPU.

cpu_present_map: Bitmap of CPUs currently present in the system. Not all
of them may be online. When physical hotplug is processed by the relevant
subsystem (e.g ACPI) can change and new bit either be added or removed
from the map depending on the event is hot-add/hot-remove. There are currently
no locking rules as of now. Typical usage is to init topology during boot,
at which time hotplug is disabled.

You really dont need to manipulate any of the system cpu maps. They should
be read-only for most use. When setting up per-cpu resources almost always use
cpu_possible_map/for_each_possible_cpu() to iterate.

Never use anything other than cpumask_t to represent bitmap of CPUs.

	#include <linux/cpumask.h>

	for_each_possible_cpu     - Iterate over cpu_possible_map
	for_each_online_cpu       - Iterate over cpu_online_map
	for_each_present_cpu      - Iterate over cpu_present_map
	for_each_cpu_mask(x,mask) - Iterate over some random collection of cpu mask.

	#include <linux/cpu.h>
	get_online_cpus() and put_online_cpus():

The above calls are used to inhibit cpu hotplug operations. While the
cpu_hotplug.refcount is non zero, the cpu_online_map will not change.
If you merely need to avoid cpus going away, you could also use
preempt_disable() and preempt_enable() for those sections.
Just remember the critical section cannot call any
function that can sleep or schedule this process away. The preempt_disable()
will work as long as stop_machine_run() is used to take a cpu down.

CPU Hotplug - Frequently Asked Questions.

Q: How to enable my kernel to support CPU hotplug?
A: When doing make defconfig, Enable CPU hotplug support

   "Processor type and Features" -> Support for Hotpluggable CPUs

Make sure that you have CONFIG_HOTPLUG, and CONFIG_SMP turned on as well.

You would need to enable CONFIG_HOTPLUG_CPU for SMP suspend/resume support
as well.

Q: What architectures support CPU hotplug?
A: As of 2.6.14, the following architectures support CPU hotplug.

i386 (Intel), ppc, ppc64, parisc, s390, ia64 and x86_64

Q: How to test if hotplug is supported on the newly built kernel?
A: You should now notice an entry in sysfs.

Check if sysfs is mounted, using the "mount" command. You should notice
an entry as shown below in the output.

	....
	none on /sys type sysfs (rw)
	....

If this is not mounted, do the following.

	 #mkdir /sysfs
	#mount -t sysfs sys /sys

Now you should see entries for all present cpu, the following is an example
in a 8-way system.