Merge tag 'docs-5.1' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "A fairly routine cycle for docs - lots of typo fixes, some new
  documents, and more translations. There's also some LICENSES
  adjustments from Thomas"

* tag 'docs-5.1' of git://git.lwn.net/linux: (74 commits)
  docs: Bring some order to filesystem documentation
  Documentation/locking/lockdep: Drop last two chars of sample states
  doc: rcu: Suspicious RCU usage is a warning
  docs: driver-api: iio: fix errors in documentation
  Documentation/process/howto: Update for 4.x -> 5.x versioning
  docs: Explicitly state that the 'Fixes:' tag shouldn't split lines
  doc: security: Add kern-doc for lsm_hooks.h
  doc: sctp: Merge and clean up rst files
  Docs: Correct /proc/stat path
  scripts/spdxcheck.py: fix C++ comment style detection
  doc: fix typos in license-rules.rst
  Documentation: fix admin-guide/README.rst minimum gcc version requirement
  doc: process: complete removal of info about -git patches
  doc: translations: sync translations 'remove info about -git patches'
  perf-security: wrap paragraphs on 72 columns
  perf-security: elaborate on perf_events/Perf privileged users
  perf-security: document collected perf_events/Perf data categories
  perf-security: document perf_events/Perf resource control
  sysfs.txt: add note on available attribute macros
  docs: kernel-doc: typo "if ... if" -> "if ... is"
  ...

Documentation/DMA-API.txt

@@ -530,8 +530,8 @@ that simply cannot make consistent memory.
 	dma_free_attrs(struct device *dev, size_t size, void *cpu_addr,
 		       dma_addr_t dma_handle, unsigned long attrs)
 
-Free memory allocated by the dma_alloc_attrs().  All parameters common
-parameters must identical to those otherwise passed to dma_fre_coherent,
+Free memory allocated by the dma_alloc_attrs().  All common
+parameters must be identical to those otherwise passed to dma_free_coherent,
 and the attrs argument must be identical to the attrs passed to
 dma_alloc_attrs().
 
@@ -717,7 +717,7 @@ dma-api/num_free_entries	The current number of free dma_debug_entries
 dma-api/nr_total_entries	The total number of dma_debug_entries in the
 				allocator, both free and used.
 
-dma-api/driver-filter		You can write a name of a driver into this file
+dma-api/driver_filter		You can write a name of a driver into this file
 				to limit the debug output to requests from that
 				particular driver. Write an empty string to
 				that file to disable the filter and see

Documentation/DMA-ISA-LPC.txt

@@ -52,8 +52,8 @@ Address translation
 -------------------
 
 To translate the virtual address to a bus address, use the normal DMA
-API. Do _not_ use isa_virt_to_phys() even though it does the same
-thing. The reason for this is that the function isa_virt_to_phys()
+API. Do _not_ use isa_virt_to_bus() even though it does the same
+thing. The reason for this is that the function isa_virt_to_bus()
 will require a Kconfig dependency to ISA, not just ISA_DMA_API which
 is really all you need. Remember that even though the DMA controller
 has its origins in ISA it is used elsewhere.

Documentation/RCU/lockdep-splat.txt

@@ -14,21 +14,21 @@ being the real world and all that.
 So let's look at an example RCU lockdep splat from 3.0-rc5, one that
 has long since been fixed:
 
-===============================
-[ INFO: suspicious RCU usage. ]
--------------------------------
+=============================
+WARNING: suspicious RCU usage
+-----------------------------
 block/cfq-iosched.c:2776 suspicious rcu_dereference_protected() usage!
 
 other info that might help us debug this:
 
 
 rcu_scheduler_active = 1, debug_locks = 0
 3 locks held by scsi_scan_6/1552:
- #0:  (&shost->scan_mutex){+.+.+.}, at: [<ffffffff8145efca>]
+ #0:  (&shost->scan_mutex){+.+.}, at: [<ffffffff8145efca>]
 scsi_scan_host_selected+0x5a/0x150
- #1:  (&eq->sysfs_lock){+.+...}, at: [<ffffffff812a5032>]
+ #1:  (&eq->sysfs_lock){+.+.}, at: [<ffffffff812a5032>]
 elevator_exit+0x22/0x60
- #2:  (&(&q->__queue_lock)->rlock){-.-...}, at: [<ffffffff812b6233>]
+ #2:  (&(&q->__queue_lock)->rlock){-.-.}, at: [<ffffffff812b6233>]
 cfq_exit_queue+0x43/0x190
 
 stack backtrace:

Documentation/admin-guide/README.rst

@@ -251,7 +251,7 @@ Configuring the kernel
 Compiling the kernel
 --------------------
 
- - Make sure you have at least gcc 3.2 available.
+ - Make sure you have at least gcc 4.6 available.
    For more information, refer to :ref:`Documentation/process/changes.rst <changes>`.
 
    Please note that you can still run a.out user programs with this kernel.

Documentation/admin-guide/kernel-parameters.txt

@@ -1197,9 +1197,10 @@
 			arch/x86/kernel/cpu/cpufreq/elanfreq.c.
 
 	elevator=	[IOSCHED]
-			Format: {"cfq" | "deadline" | "noop"}
-			See Documentation/block/cfq-iosched.txt and
-			Documentation/block/deadline-iosched.txt for details.
+			Format: { "mq-deadline" | "kyber" | "bfq" }
+			See Documentation/block/deadline-iosched.txt,
+			Documentation/block/kyber-iosched.txt and
+			Documentation/block/bfq-iosched.txt for details.
 
 	elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
 			Specifies physical address of start of kernel core
@@ -1996,6 +1997,12 @@
 			Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
 			the default is off.
 
+	kpti=		[ARM64] Control page table isolation of user
+			and kernel address spaces.
+			Default: enabled on cores which need mitigation.
+			0: force disabled
+			1: force enabled
+
 	kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
 			Default is 0 (don't ignore, but inject #GP)
 

Documentation/admin-guide/perf-security.rst

@@ -6,83 +6,211 @@ Perf Events and tool security
 Overview
 --------
 
-Usage of Performance Counters for Linux (perf_events) [1]_ , [2]_ , [3]_ can
-impose a considerable risk of leaking sensitive data accessed by monitored
-processes. The data leakage is possible both in scenarios of direct usage of
-perf_events system call API [2]_ and over data files generated by Perf tool user
-mode utility (Perf) [3]_ , [4]_ . The risk depends on the nature of data that
-perf_events performance monitoring units (PMU) [2]_ collect and expose for
-performance analysis. Having that said perf_events/Perf performance monitoring
-is the subject for security access control management [5]_ .
+Usage of Performance Counters for Linux (perf_events) [1]_ , [2]_ , [3]_
+can impose a considerable risk of leaking sensitive data accessed by
+monitored processes. The data leakage is possible both in scenarios of
+direct usage of perf_events system call API [2]_ and over data files
+generated by Perf tool user mode utility (Perf) [3]_ , [4]_ . The risk
+depends on the nature of data that perf_events performance monitoring
+units (PMU) [2]_ and Perf collect and expose for performance analysis.
+Collected system and performance data may be split into several
+categories:
+
+1. System hardware and software configuration data, for example: a CPU
+   model and its cache configuration, an amount of available memory and
+   its topology, used kernel and Perf versions, performance monitoring
+   setup including experiment time, events configuration, Perf command
+   line parameters, etc.
+
+2. User and kernel module paths and their load addresses with sizes,
+   process and thread names with their PIDs and TIDs, timestamps for
+   captured hardware and software events.
+
+3. Content of kernel software counters (e.g., for context switches, page
+   faults, CPU migrations), architectural hardware performance counters
+   (PMC) [8]_ and machine specific registers (MSR) [9]_ that provide
+   execution metrics for various monitored parts of the system (e.g.,
+   memory controller (IMC), interconnect (QPI/UPI) or peripheral (PCIe)
+   uncore counters) without direct attribution to any execution context
+   state.
+
+4. Content of architectural execution context registers (e.g., RIP, RSP,
+   RBP on x86_64), process user and kernel space memory addresses and
+   data, content of various architectural MSRs that capture data from
+   this category.
+
+Data that belong to the fourth category can potentially contain
+sensitive process data. If PMUs in some monitoring modes capture values
+of execution context registers or data from process memory then access
+to such monitoring capabilities requires to be ordered and secured
+properly. So, perf_events/Perf performance monitoring is the subject for
+security access control management [5]_ .
 
 perf_events/Perf access control
 -------------------------------
 
-To perform security checks, the Linux implementation splits processes into two
-categories [6]_ : a) privileged processes (whose effective user ID is 0, referred
-to as superuser or root), and b) unprivileged processes (whose effective UID is
-nonzero). Privileged processes bypass all kernel security permission checks so
-perf_events performance monitoring is fully available to privileged processes
-without access, scope and resource restrictions.
-
-Unprivileged processes are subject to a full security permission check based on
-the process's credentials [5]_ (usually: effective UID, effective GID, and
-supplementary group list).
-
-Linux divides the privileges traditionally associated with superuser into
-distinct units, known as capabilities [6]_ , which can be independently enabled
-and disabled on per-thread basis for processes and files of unprivileged users.
-
-Unprivileged processes with enabled CAP_SYS_ADMIN capability are treated as
-privileged processes with respect to perf_events performance monitoring and
-bypass *scope* permissions checks in the kernel.
-
-Unprivileged processes using perf_events system call API is also subject for
-PTRACE_MODE_READ_REALCREDS ptrace access mode check [7]_ , whose outcome
-determines whether monitoring is permitted. So unprivileged processes provided
-with CAP_SYS_PTRACE capability are effectively permitted to pass the check.
-
-Other capabilities being granted to unprivileged processes can effectively
-enable capturing of additional data required for later performance analysis of
-monitored processes or a system. For example, CAP_SYSLOG capability permits
-reading kernel space memory addresses from /proc/kallsyms file.
+To perform security checks, the Linux implementation splits processes
+into two categories [6]_ : a) privileged processes (whose effective user
+ID is 0, referred to as superuser or root), and b) unprivileged
+processes (whose effective UID is nonzero). Privileged processes bypass
+all kernel security permission checks so perf_events performance
+monitoring is fully available to privileged processes without access,
+scope and resource restrictions.
+
+Unprivileged processes are subject to a full security permission check
+based on the process's credentials [5]_ (usually: effective UID,
+effective GID, and supplementary group list).
+
+Linux divides the privileges traditionally associated with superuser
+into distinct units, known as capabilities [6]_ , which can be
+independently enabled and disabled on per-thread basis for processes and
+files of unprivileged users.
+
+Unprivileged processes with enabled CAP_SYS_ADMIN capability are treated
+as privileged processes with respect to perf_events performance
+monitoring and bypass *scope* permissions checks in the kernel.
+
+Unprivileged processes using perf_events system call API is also subject
+for PTRACE_MODE_READ_REALCREDS ptrace access mode check [7]_ , whose
+outcome determines whether monitoring is permitted. So unprivileged
+processes provided with CAP_SYS_PTRACE capability are effectively
+permitted to pass the check.
+
+Other capabilities being granted to unprivileged processes can
+effectively enable capturing of additional data required for later
+performance analysis of monitored processes or a system. For example,
+CAP_SYSLOG capability permits reading kernel space memory addresses from
+/proc/kallsyms file.
+
+perf_events/Perf privileged users
+---------------------------------
+
+Mechanisms of capabilities, privileged capability-dumb files [6]_ and
+file system ACLs [10]_ can be used to create a dedicated group of
+perf_events/Perf privileged users who are permitted to execute
+performance monitoring without scope limits. The following steps can be
+taken to create such a group of privileged Perf users.
+
+1. Create perf_users group of privileged Perf users, assign perf_users
+   group to Perf tool executable and limit access to the executable for
+   other users in the system who are not in the perf_users group:
+
+::
+
+   # groupadd perf_users
+   # ls -alhF
+   -rwxr-xr-x  2 root root  11M Oct 19 15:12 perf
+   # chgrp perf_users perf
+   # ls -alhF
+   -rwxr-xr-x  2 root perf_users  11M Oct 19 15:12 perf
+   # chmod o-rwx perf
+   # ls -alhF
+   -rwxr-x---  2 root perf_users  11M Oct 19 15:12 perf
+
+2. Assign the required capabilities to the Perf tool executable file and
+   enable members of perf_users group with performance monitoring
+   privileges [6]_ :
+
+::
+
+   # setcap "cap_sys_admin,cap_sys_ptrace,cap_syslog=ep" perf
+   # setcap -v "cap_sys_admin,cap_sys_ptrace,cap_syslog=ep" perf
+   perf: OK
+   # getcap perf
+   perf = cap_sys_ptrace,cap_sys_admin,cap_syslog+ep
+
+As a result, members of perf_users group are capable of conducting
+performance monitoring by using functionality of the configured Perf
+tool executable that, when executes, passes perf_events subsystem scope
+checks.
+
+This specific access control management is only available to superuser
+or root running processes with CAP_SETPCAP, CAP_SETFCAP [6]_
+capabilities.
 
 perf_events/Perf unprivileged users
 -----------------------------------
 
-perf_events/Perf *scope* and *access* control for unprivileged processes is
-governed by perf_event_paranoid [2]_ setting:
+perf_events/Perf *scope* and *access* control for unprivileged processes
+is governed by perf_event_paranoid [2]_ setting:
 
 -1:
-     Impose no *scope* and *access* restrictions on using perf_events performance
-     monitoring. Per-user per-cpu perf_event_mlock_kb [2]_ locking limit is
-     ignored when allocating memory buffers for storing performance data.
-     This is the least secure mode since allowed monitored *scope* is
-     maximized and no perf_events specific limits are imposed on *resources*
-     allocated for performance monitoring.
+     Impose no *scope* and *access* restrictions on using perf_events
+     performance monitoring. Per-user per-cpu perf_event_mlock_kb [2]_
+     locking limit is ignored when allocating memory buffers for storing
+     performance data. This is the least secure mode since allowed
+     monitored *scope* is maximized and no perf_events specific limits
+     are imposed on *resources* allocated for performance monitoring.
 
 >=0:
      *scope* includes per-process and system wide performance monitoring
-     but excludes raw tracepoints and ftrace function tracepoints monitoring.
-     CPU and system events happened when executing either in user or
-     in kernel space can be monitored and captured for later analysis.
-     Per-user per-cpu perf_event_mlock_kb locking limit is imposed but
-     ignored for unprivileged processes with CAP_IPC_LOCK [6]_ capability.
+     but excludes raw tracepoints and ftrace function tracepoints
+     monitoring. CPU and system events happened when executing either in
+     user or in kernel space can be monitored and captured for later
+     analysis. Per-user per-cpu perf_event_mlock_kb locking limit is
+     imposed but ignored for unprivileged processes with CAP_IPC_LOCK
+     [6]_ capability.
 
 >=1:
-     *scope* includes per-process performance monitoring only and excludes
-     system wide performance monitoring. CPU and system events happened when
-     executing either in user or in kernel space can be monitored and
-     captured for later analysis. Per-user per-cpu perf_event_mlock_kb
-     locking limit is imposed but ignored for unprivileged processes with
-     CAP_IPC_LOCK capability.
+     *scope* includes per-process performance monitoring only and
+     excludes system wide performance monitoring. CPU and system events
+     happened when executing either in user or in kernel space can be
+     monitored and captured for later analysis. Per-user per-cpu
+     perf_event_mlock_kb locking limit is imposed but ignored for
+     unprivileged processes with CAP_IPC_LOCK capability.
 
 >=2:
-     *scope* includes per-process performance monitoring only. CPU and system
-     events happened when executing in user space only can be monitored and
-     captured for later analysis. Per-user per-cpu perf_event_mlock_kb
-     locking limit is imposed but ignored for unprivileged processes with
-     CAP_IPC_LOCK capability.
+     *scope* includes per-process performance monitoring only. CPU and
+     system events happened when executing in user space only can be
+     monitored and captured for later analysis. Per-user per-cpu
+     perf_event_mlock_kb locking limit is imposed but ignored for
+     unprivileged processes with CAP_IPC_LOCK capability.
+
+perf_events/Perf resource control
+---------------------------------
+
+Open file descriptors
++++++++++++++++++++++
+
+The perf_events system call API [2]_ allocates file descriptors for
+every configured PMU event. Open file descriptors are a per-process
+accountable resource governed by the RLIMIT_NOFILE [11]_ limit
+(ulimit -n), which is usually derived from the login shell process. When
+configuring Perf collection for a long list of events on a large server
+system, this limit can be easily hit preventing required monitoring
+configuration. RLIMIT_NOFILE limit can be increased on per-user basis
+modifying content of the limits.conf file [12]_ . Ordinarily, a Perf
+sampling session (perf record) requires an amount of open perf_event
+file descriptors that is not less than the number of monitored events
+multiplied by the number of monitored CPUs.
+
+Memory allocation
++++++++++++++++++
+
+The amount of memory available to user processes for capturing
+performance monitoring data is governed by the perf_event_mlock_kb [2]_
+setting. This perf_event specific resource setting defines overall
+per-cpu limits of memory allowed for mapping by the user processes to
+execute performance monitoring. The setting essentially extends the
+RLIMIT_MEMLOCK [11]_ limit, but only for memory regions mapped
+specifically for capturing monitored performance events and related data.
+
+For example, if a machine has eight cores and perf_event_mlock_kb limit
+is set to 516 KiB, then a user process is provided with 516 KiB * 8 =
+4128 KiB of memory above the RLIMIT_MEMLOCK limit (ulimit -l) for
+perf_event mmap buffers. In particular, this means that, if the user
+wants to start two or more performance monitoring processes, the user is
+required to manually distribute the available 4128 KiB between the
+monitoring processes, for example, using the --mmap-pages Perf record
+mode option. Otherwise, the first started performance monitoring process
+allocates all available 4128 KiB and the other processes will fail to
+proceed due to the lack of memory.
+
+RLIMIT_MEMLOCK and perf_event_mlock_kb resource constraints are ignored
+for processes with the CAP_IPC_LOCK capability. Thus, perf_events/Perf
+privileged users can be provided with memory above the constraints for
+perf_events/Perf performance monitoring purpose by providing the Perf
+executable with CAP_IPC_LOCK capability.
 
 Bibliography
 ------------
@@ -94,4 +222,9 @@ Bibliography
 .. [5] `<https://www.kernel.org/doc/html/latest/security/credentials.html>`_
 .. [6] `<http://man7.org/linux/man-pages/man7/capabilities.7.html>`_
 .. [7] `<http://man7.org/linux/man-pages/man2/ptrace.2.html>`_
+.. [8] `<https://en.wikipedia.org/wiki/Hardware_performance_counter>`_
+.. [9] `<https://en.wikipedia.org/wiki/Model-specific_register>`_
+.. [10] `<http://man7.org/linux/man-pages/man5/acl.5.html>`_
+.. [11] `<http://man7.org/linux/man-pages/man2/getrlimit.2.html>`_
+.. [12] `<http://man7.org/linux/man-pages/man5/limits.conf.5.html>`_