1 files changed, 33 insertions, 13 deletions

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 322a00bb99d9..3e5b63ebb821 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -19,6 +19,7 @@ Currently, these files might (depending on your configuration)
 show up in /proc/sys/kernel:
 - acpi_video_flags
 - acct
+- callhome                   [ S390 only ]
 - auto_msgmni
 - core_pattern
 - core_uses_pid
@@ -91,6 +92,21 @@ valid for 30 seconds.
 
 ==============================================================
 
+callhome:
+
+Controls the kernel's callhome behavior in case of a kernel panic.
+
+The s390 hardware allows an operating system to send a notification
+to a service organization (callhome) in case of an operating system panic.
+
+When the value in this file is 0 (which is the default behavior)
+nothing happens in case of a kernel panic. If this value is set to "1"
+the complete kernel oops message is send to the IBM customer service
+organization in case the mainframe the Linux operating system is running
+on has a service contract with IBM.
+
+==============================================================
+
 core_pattern:
 
 core_pattern is used to specify a core dumpfile pattern name.
@@ -303,25 +319,29 @@ This option can be used to select the type of process address
 space randomization that is used in the system, for architectures
 that support this feature.
 
-0 - Turn the process address space randomization off by default.
+0 - Turn the process address space randomization off.  This is the
+    default for architectures that do not support this feature anyways,
+    and kernels that are booted with the "norandmaps" parameter.
 
 1 - Make the addresses of mmap base, stack and VDSO page randomized.
     This, among other things, implies that shared libraries will be
-    loaded to random addresses. Also for PIE-linked binaries, the location
-    of code start is randomized.
+    loaded to random addresses.  Also for PIE-linked binaries, the
+    location of code start is randomized.  This is the default if the
+    CONFIG_COMPAT_BRK option is enabled.
 
-    With heap randomization, the situation is a little bit more
-    complicated.
-    There a few legacy applications out there (such as some ancient
+2 - Additionally enable heap randomization.  This is the default if
+    CONFIG_COMPAT_BRK is disabled.
+
+    There are a few legacy applications out there (such as some ancient
     versions of libc.so.5 from 1996) that assume that brk area starts
-    just after the end of the code+bss. These applications break when
-    start of the brk area is randomized. There are however no known
+    just after the end of the code+bss.  These applications break when
+    start of the brk area is randomized.  There are however no known
     non-legacy applications that would be broken this way, so for most
-    systems it is safe to choose full randomization. However there is
-    a CONFIG_COMPAT_BRK option for systems with ancient and/or broken
-    binaries, that makes heap non-randomized, but keeps all other
-    parts of process address space randomized if randomize_va_space
-    sysctl is turned on.
+    systems it is safe to choose full randomization.
+
+    Systems with ancient and/or broken binaries should be configured
+    with CONFIG_COMPAT_BRK enabled, which excludes the heap from process
+    address space randomization.
 
 ==============================================================