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-rw-r--r--Documentation/arch/riscv/cmodx.rst46
-rw-r--r--Documentation/arch/riscv/hwprobe.rst26
2 files changed, 65 insertions, 7 deletions
diff --git a/Documentation/arch/riscv/cmodx.rst b/Documentation/arch/riscv/cmodx.rst
index 8c48bcff3df9..40ba53bed5df 100644
--- a/Documentation/arch/riscv/cmodx.rst
+++ b/Documentation/arch/riscv/cmodx.rst
@@ -10,13 +10,45 @@ modified by the program itself. Instruction storage and the instruction cache
program must enforce its own synchronization with the unprivileged fence.i
instruction.
-However, the default Linux ABI prohibits the use of fence.i in userspace
-applications. At any point the scheduler may migrate a task onto a new hart. If
-migration occurs after the userspace synchronized the icache and instruction
-storage with fence.i, the icache on the new hart will no longer be clean. This
-is due to the behavior of fence.i only affecting the hart that it is called on.
-Thus, the hart that the task has been migrated to may not have synchronized
-instruction storage and icache.
+CMODX in the Kernel Space
+-------------------------
+
+Dynamic ftrace
+---------------------
+
+Essentially, dynamic ftrace directs the control flow by inserting a function
+call at each patchable function entry, and patches it dynamically at runtime to
+enable or disable the redirection. In the case of RISC-V, 2 instructions,
+AUIPC + JALR, are required to compose a function call. However, it is impossible
+to patch 2 instructions and expect that a concurrent read-side executes them
+without a race condition. This series makes atmoic code patching possible in
+RISC-V ftrace. Kernel preemption makes things even worse as it allows the old
+state to persist across the patching process with stop_machine().
+
+In order to get rid of stop_machine() and run dynamic ftrace with full kernel
+preemption, we partially initialize each patchable function entry at boot-time,
+setting the first instruction to AUIPC, and the second to NOP. Now, atmoic
+patching is possible because the kernel only has to update one instruction.
+According to Ziccif, as long as an instruction is naturally aligned, the ISA
+guarantee an atomic update.
+
+By fixing down the first instruction, AUIPC, the range of the ftrace trampoline
+is limited to +-2K from the predetermined target, ftrace_caller, due to the lack
+of immediate encoding space in RISC-V. To address the issue, we introduce
+CALL_OPS, where an 8B naturally align metadata is added in front of each
+pacthable function. The metadata is resolved at the first trampoline, then the
+execution can be derect to another custom trampoline.
+
+CMODX in the User Space
+-----------------------
+
+Though fence.i is an unprivileged instruction, the default Linux ABI prohibits
+the use of fence.i in userspace applications. At any point the scheduler may
+migrate a task onto a new hart. If migration occurs after the userspace
+synchronized the icache and instruction storage with fence.i, the icache on the
+new hart will no longer be clean. This is due to the behavior of fence.i only
+affecting the hart that it is called on. Thus, the hart that the task has been
+migrated to may not have synchronized instruction storage and icache.
There are two ways to solve this problem: use the riscv_flush_icache() syscall,
or use the ``PR_RISCV_SET_ICACHE_FLUSH_CTX`` prctl() and emit fence.i in
diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
index f60bf5991755..2aa9be272d5d 100644
--- a/Documentation/arch/riscv/hwprobe.rst
+++ b/Documentation/arch/riscv/hwprobe.rst
@@ -271,6 +271,10 @@ The following keys are defined:
* :c:macro:`RISCV_HWPROBE_EXT_ZICBOM`: The Zicbom extension is supported, as
ratified in commit 3dd606f ("Create cmobase-v1.0.pdf") of riscv-CMOs.
+ * :c:macro:`RISCV_HWPROBE_EXT_ZABHA`: The Zabha extension is supported as
+ ratified in commit 49f49c842ff9 ("Update to Rafified state") of
+ riscv-zabha.
+
* :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: Deprecated. Returns similar values to
:c:macro:`RISCV_HWPROBE_KEY_MISALIGNED_SCALAR_PERF`, but the key was
mistakenly classified as a bitmask rather than a value.
@@ -335,3 +339,25 @@ The following keys are defined:
* :c:macro:`RISCV_HWPROBE_KEY_ZICBOM_BLOCK_SIZE`: An unsigned int which
represents the size of the Zicbom block in bytes.
+
+* :c:macro:`RISCV_HWPROBE_KEY_VENDOR_EXT_SIFIVE_0`: A bitmask containing the
+ sifive vendor extensions that are compatible with the
+ :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`: base system behavior.
+
+ * SIFIVE
+
+ * :c:macro:`RISCV_HWPROBE_VENDOR_EXT_XSFVQMACCDOD`: The Xsfqmaccdod vendor
+ extension is supported in version 1.1 of SiFive Int8 Matrix Multiplication
+ Extensions Specification.
+
+ * :c:macro:`RISCV_HWPROBE_VENDOR_EXT_XSFVQMACCQOQ`: The Xsfqmaccqoq vendor
+ extension is supported in version 1.1 of SiFive Int8 Matrix Multiplication
+ Instruction Extensions Specification.
+
+ * :c:macro:`RISCV_HWPROBE_VENDOR_EXT_XSFVFNRCLIPXFQF`: The Xsfvfnrclipxfqf
+ vendor extension is supported in version 1.0 of SiFive FP32-to-int8 Ranged
+ Clip Instructions Extensions Specification.
+
+ * :c:macro:`RISCV_HWPROBE_VENDOR_EXT_XSFVFWMACCQQQ`: The Xsfvfwmaccqqq
+ vendor extension is supported in version 1.0 of Matrix Multiply Accumulate
+ Instruction Extensions Specification. \ No newline at end of file