[PATCH v2] docs: sysctl/kernel: document unaligned controls

[Stephen Kitt <steve@sk2.org>]

This documents ignore-unaligned-usertrap, unaligned-dump-stack, and
unaligned-trap, based on arch/arc/kernel/unaligned.c,
arch/ia64/kernel/unaligned.c, and arch/parisc/kernel/unaligned.c.

While we're at it, integrate unaligned-memory-access.txt into the docs
tree.

Signed-off-by: Stephen Kitt <steve@sk2.org>
---
Changes since v1:
  - move unaligned-memory-access.txt to process/
  - removed UTF-8 apostrophe from the commit message

 Documentation/admin-guide/sysctl/kernel.rst   | 51 +++++++++++++++++++
 Documentation/process/index.rst               |  1 +
 .../unaligned-memory-access.rst}              |  0
 3 files changed, 52 insertions(+)
 rename Documentation/{unaligned-memory-access.txt => process/unaligned-memory-access.rst} (100%)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index eb6bc9cc0318..4bb4d55f20ff 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -402,6 +402,25 @@ Controls whether the panic kmsg data should be reported to Hyper-V.
 = =========================================================
 
 
+ignore-unaligned-usertrap
+=========================
+
+On architectures where unaligned accesses cause traps, and where this
+feature is supported (``CONFIG_SYSCTL_ARCH_UNALIGN_NO_WARN``;
+currently, ``arc`` and ``ia64``), controls whether all unaligned traps
+are logged.
+
+= =============================================================
+0 Log all unaligned accesses.
+1 Only warn the first time a process traps. This is the default
+  setting.
+= =============================================================
+
+See also `unaligned-trap`_ and `unaligned-dump-stack`_. On ``ia64``,
+this allows system administrators to override the
+``IA64_THREAD_UAC_NOPRINT`` ``prctl`` and avoid logs being flooded.
+
+
 kexec_load_disabled
 ===================
 
@@ -1252,6 +1271,38 @@ See :doc:`/admin-guide/kernel-parameters` and
 :doc:`/trace/boottime-trace`.
 
 
+.. _unaligned-dump-stack:
+
+unaligned-dump-stack (ia64)
+===========================
+
+When logging unaligned accesses, controls whether the stack is
+dumped.
+
+= ===================================================
+0 Do not dump the stack. This is the default setting.
+1 Dump the stack.
+= ===================================================
+
+See also `ignore-unaligned-usertrap`_.
+
+
+unaligned-trap
+==============
+
+On architectures where unaligned accesses cause traps, and where this
+feature is supported (``CONFIG_SYSCTL_ARCH_UNALIGN_ALLOW``; currently,
+``arc`` and ``parisc``), controls whether unaligned traps are caught
+and emulated (instead of failing).
+
+= ========================================================
+0 Do not emulate unaligned accesses.
+1 Emulate unaligned accesses. This is the default setting.
+= ========================================================
+
+See also `ignore-unaligned-usertrap`_.
+
+
 unknown_nmi_panic
 =================
 
diff --git a/Documentation/process/index.rst b/Documentation/process/index.rst
index 6399d92f0b21..f07c9250c3ac 100644
--- a/Documentation/process/index.rst
+++ b/Documentation/process/index.rst
@@ -61,6 +61,7 @@ lack of a better place.
    botching-up-ioctls
    clang-format
    ../riscv/patch-acceptance
+   unaligned-memory-access
 
 .. only::  subproject and html
 
diff --git a/Documentation/unaligned-memory-access.txt b/Documentation/process/unaligned-memory-access.rst
similarity index 100%
rename from Documentation/unaligned-memory-access.txt
rename to Documentation/process/unaligned-memory-access.rst

base-commit: 56b62540782bfde459acc8eb15b949eaf151c881
-- 
2.20.1