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2024-12-19 9370bb92b2d16684ee45cf24e879c93c509162da 
 kernel/tools/memory-model/README
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2020 REQUIREMENTS
2121 ============
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-Version 7.49 of the "herd7" and "klitmus7" tools must be downloaded
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-separately:
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+Version 7.52 or higher of the "herd7" and "klitmus7" tools must be
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+downloaded separately:
2525 
2626   https://github.com/herd/herdtools7
2727 
2828 See "herdtools7/INSTALL.md" for installation instructions.
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+
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+Note that although these tools usually provide backwards compatibility,
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+this is not absolutely guaranteed.
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+
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+For example, a future version of herd7 might not work with the model
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+in this release.  A compatible model will likely be made available in
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+a later release of Linux kernel.
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+
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+If you absolutely need to run the model in this particular release,
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+please try using the exact version called out above.
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+
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+klitmus7 is independent of the model provided here.  It has its own
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+dependency on a target kernel release where converted code is built
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+and executed.  Any change in kernel APIs essential to klitmus7 will
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+necessitate an upgrade of klitmus7.
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+
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+If you find any compatibility issues in klitmus7, please inform the
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+memory model maintainers.
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+
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+klitmus7 Compatibility Table
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+----------------------------
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+
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+	============  ==========
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+	target Linux  herdtools7
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+	------------  ----------
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+	     -- 4.18  7.48 --
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+	4.15 -- 4.19  7.49 --
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+	4.20 -- 5.5   7.54 --
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+	5.6  --       7.56 --
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+	============  ==========
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3060 
3161 ==================
....@@ -33,10 +63,32 @@
3363 ==================
3464 
3565 The memory model is used, in conjunction with "herd7", to exhaustively
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-explore the state space of small litmus tests.
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+explore the state space of small litmus tests.  Documentation describing
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+the format, features, capabilities and limitations of these litmus
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+tests is available in tools/memory-model/Documentation/litmus-tests.txt.
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-For example, to run SB+fencembonceonces.litmus against the memory model:
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+Example litmus tests may be found in the Linux-kernel source tree:
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+	tools/memory-model/litmus-tests/
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+	Documentation/litmus-tests/
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+
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+Several thousand more example litmus tests are available here:
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+
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+	https://github.com/paulmckrcu/litmus
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+	https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/perfbook.git/tree/CodeSamples/formal/herd
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+	https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/perfbook.git/tree/CodeSamples/formal/litmus
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+
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+Documentation describing litmus tests and now to use them may be found
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+here:
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+
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+	tools/memory-model/Documentation/litmus-tests.txt
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+
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+The remainder of this section uses the SB+fencembonceonces.litmus test
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+located in the tools/memory-model directory.
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+
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+To run SB+fencembonceonces.litmus against the memory model:
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+
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+  $ cd $LINUX_SOURCE_TREE/tools/memory-model
4092   $ herd7 -conf linux-kernel.cfg litmus-tests/SB+fencembonceonces.litmus
4193 
4294 Here is the corresponding output:
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57109 The "Positive: 0 Negative: 3" and the "Never 0 3" each indicate that
58110 this litmus test's "exists" clause can not be satisfied.
59111 
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-See "herd7 -help" or "herdtools7/doc/" for more information.
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+See "herd7 -help" or "herdtools7/doc/" for more information on running the
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+tool itself, but please be aware that this documentation is intended for
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+people who work on the memory model itself, that is, people making changes
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+to the tools/memory-model/linux-kernel.* files.  It is not intended for
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+people focusing on writing, understanding, and running LKMM litmus tests.
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62118 
63119 =====================
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94150 test's "exists" clause was not reached.
95151 
96152 And, as with "herd7", please see "klitmus7 -help" or "herdtools7/doc/"
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-for more information.
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+for more information.  And again, please be aware that this documentation
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+is intended for people who work on the memory model itself, that is,
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+people making changes to the tools/memory-model/linux-kernel.* files.
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+It is not intended for people focusing on writing, understanding, and
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+running LKMM litmus tests.
98158 
99159 
100160 ====================
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107167 Documentation/explanation.txt
108168 	Describes the memory model in detail.
109169 
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+Documentation/litmus-tests.txt
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+	Describes the format, features, capabilities, and limitations
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+	of the litmus tests that LKMM can evaluate.
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+
110174 Documentation/recipes.txt
111175 	Lists common memory-ordering patterns.
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113177 Documentation/references.txt
114178 	Provides background reading.
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+
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+Documentation/simple.txt
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+	Starting point for someone new to Linux-kernel concurrency.
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+	And also for those needing a reminder of the simpler approaches
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+	to concurrency!
115184 
116185 linux-kernel.bell
117186 	Categorizes the relevant instructions, including memory
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156225 README
157226 	This file.
158227 
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-
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-===========
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-LIMITATIONS
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-===========
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-
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-The Linux-kernel memory model has the following limitations:
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-
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-1.	Compiler optimizations are not modeled.  Of course, the use
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-	of READ_ONCE() and WRITE_ONCE() limits the compiler's ability
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-	to optimize, but there is Linux-kernel code that uses bare C
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-	memory accesses.  Handling this code is on the to-do list.
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-	For more information, see Documentation/explanation.txt (in
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-	particular, the "THE PROGRAM ORDER RELATION: po AND po-loc"
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-	and "A WARNING" sections).
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-
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-2.	Multiple access sizes for a single variable are not supported,
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-	and neither are misaligned or partially overlapping accesses.
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-
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-3.	Exceptions and interrupts are not modeled.  In some cases,
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-	this limitation can be overcome by modeling the interrupt or
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-	exception with an additional process.
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-
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-4.	I/O such as MMIO or DMA is not supported.
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-
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-5.	Self-modifying code (such as that found in the kernel's
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-	alternatives mechanism, function tracer, Berkeley Packet Filter
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-	JIT compiler, and module loader) is not supported.
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-
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-6.	Complete modeling of all variants of atomic read-modify-write
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-	operations, locking primitives, and RCU is not provided.
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-	For example, call_rcu() and rcu_barrier() are not supported.
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-	However, a substantial amount of support is provided for these
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-	operations, as shown in the linux-kernel.def file.
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-
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-The "herd7" tool has some additional limitations of its own, apart from
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-the memory model:
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-
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-1.	Non-trivial data structures such as arrays or structures are
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-	not supported.	However, pointers are supported, allowing trivial
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-	linked lists to be constructed.
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-
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-2.	Dynamic memory allocation is not supported, although this can
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-	be worked around in some cases by supplying multiple statically
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-	allocated variables.
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-
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-Some of these limitations may be overcome in the future, but others are
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-more likely to be addressed by incorporating the Linux-kernel memory model
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-into other tools.
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+scripts	Various scripts, see scripts/README.