Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 27 insertions, 0 deletions

diff --git a/Documentation/arch/arm/swp_emulation.rst b/Documentation/arch/arm/swp_emulation.rst
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+Software emulation of deprecated SWP instruction (CONFIG_SWP_EMULATE)
+---------------------------------------------------------------------
+
+ARMv6 architecture deprecates use of the SWP/SWPB instructions, and recommends
+moving to the load-locked/store-conditional instructions LDREX and STREX.
+
+ARMv7 multiprocessing extensions introduce the ability to disable these
+instructions, triggering an undefined instruction exception when executed.
+Trapped instructions are emulated using an LDREX/STREX or LDREXB/STREXB
+sequence. If a memory access fault (an abort) occurs, a segmentation fault is
+signalled to the triggering process.
+
+/proc/cpu/swp_emulation holds some statistics/information, including the PID of
+the last process to trigger the emulation to be invocated. For example::
+
+  Emulated SWP:		12
+  Emulated SWPB:		0
+  Aborted SWP{B}:		1
+  Last process:		314
+
+
+NOTE:
+  when accessing uncached shared regions, LDREX/STREX rely on an external
+  transaction monitoring block called a global monitor to maintain update
+  atomicity. If your system does not implement a global monitor, this option can
+  cause programs that perform SWP operations to uncached memory to deadlock, as
+  the STREX operation will always fail.