diff options
Diffstat (limited to 'Documentation/arch/riscv')
-rw-r--r-- | Documentation/arch/riscv/cmodx.rst | 46 | ||||
-rw-r--r-- | Documentation/arch/riscv/hwprobe.rst | 26 |
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.
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