We can use the PR_{S,G}ET_MEMORY_CONSISTENCY_MODEL prctl calls to change the memory consistency model at run-time if we have Ssdtso. This patch registers RISCV_WMO and RISCV_TSO as valid arguments for these prctl calls and implements the glue code to switch between these.
Signed-off-by: Christoph Müllner christoph.muellner@vrull.eu --- .../mm/dynamic-memory-consistency-model.rst | 12 +++- arch/riscv/include/asm/processor.h | 7 ++ arch/riscv/kernel/Makefile | 1 + arch/riscv/kernel/dtso.c | 67 +++++++++++++++++++ include/uapi/linux/prctl.h | 2 + 5 files changed, 88 insertions(+), 1 deletion(-) create mode 100644 arch/riscv/kernel/dtso.c
diff --git a/Documentation/mm/dynamic-memory-consistency-model.rst b/Documentation/mm/dynamic-memory-consistency-model.rst index 1fce855a1fad..c8188c174e27 100644 --- a/Documentation/mm/dynamic-memory-consistency-model.rst +++ b/Documentation/mm/dynamic-memory-consistency-model.rst @@ -73,4 +73,14 @@ Supported memory consistency models This section defines the memory consistency models which are supported by the prctl interface.
-<none> +RISC-V +------ + +RISC-V uses RVWMO (RISC-V weak memory ordering) as default memory consistency +model. TSO (total store ordering) is another specified model and provides +additional ordering guarantees. Switching user-mode processes from RVWMO to TSO +is possible when the Ssdtso extension is available. + +* :c:macro:`PR_MEMORY_CONSISTENCY_MODEL_RISCV_WMO`: RISC-V weak memory ordering (default). + +* :c:macro:`PR_MEMORY_CONSISTENCY_MODEL_RISCV_TSO`: RISC-V total store ordering. diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h index a8509cc31ab2..05e05fddc94d 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -184,6 +184,13 @@ extern int set_unalign_ctl(struct task_struct *tsk, unsigned int val); #define GET_UNALIGN_CTL(tsk, addr) get_unalign_ctl((tsk), (addr)) #define SET_UNALIGN_CTL(tsk, val) set_unalign_ctl((tsk), (val))
+#ifdef CONFIG_RISCV_ISA_SSDTSO +extern int dtso_set_memory_consistency_model(unsigned long arg); +extern int dtso_get_memory_consistency_model(void); +#define SET_MEMORY_CONSISTENCY_MODEL(arg) dtso_set_memory_consistency_model(arg) +#define GET_MEMORY_CONSISTENCY_MODEL() dtso_get_memory_consistency_model() +#endif /* CONIG_RISCV_ISA_SSDTSO */ + #endif /* __ASSEMBLY__ */
#endif /* _ASM_RISCV_PROCESSOR_H */ diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile index f71910718053..85f7291da498 100644 --- a/arch/riscv/kernel/Makefile +++ b/arch/riscv/kernel/Makefile @@ -65,6 +65,7 @@ obj-$(CONFIG_RISCV_MISALIGNED) += traps_misaligned.o obj-$(CONFIG_FPU) += fpu.o obj-$(CONFIG_RISCV_ISA_V) += vector.o obj-$(CONFIG_RISCV_ISA_V) += kernel_mode_vector.o +obj-$(CONFIG_RISCV_ISA_SSDTSO) += dtso.o obj-$(CONFIG_SMP) += smpboot.o obj-$(CONFIG_SMP) += smp.o obj-$(CONFIG_SMP) += cpu_ops.o diff --git a/arch/riscv/kernel/dtso.c b/arch/riscv/kernel/dtso.c new file mode 100644 index 000000000000..591d5f9de0f5 --- /dev/null +++ b/arch/riscv/kernel/dtso.c @@ -0,0 +1,67 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* + * Copyright (c) 2024 Christoph Muellner christoph.muellner@vrull.eu + */ + +#include <linux/cpu.h> +#include <linux/smp.h> +#include <linux/prctl.h> + +#include <asm/cpu.h> +#include <asm/dtso.h> + +#include <trace/events/ipi.h> + +int dtso_set_memory_consistency_model(unsigned long arg) +{ + int cpu; + unsigned long cur_model = get_memory_consistency_model(current); + unsigned long new_model; + + switch (arg) { + case PR_MEMORY_CONSISTENCY_MODEL_RISCV_WMO: + new_model = RISCV_MEMORY_CONSISTENCY_MODEL_WMO; + break; + case PR_MEMORY_CONSISTENCY_MODEL_RISCV_TSO: + new_model = RISCV_MEMORY_CONSISTENCY_MODEL_TSO; + break; + default: + return -EINVAL; + } + + /* No change requested. */ + if (cur_model == new_model) + return 0; + + /* Enabling TSO only works if DTSO is available. */ + if (new_model == PR_MEMORY_CONSISTENCY_MODEL_RISCV_TSO && !has_dtso()) + return -EINVAL; + + /* Switching TSO->WMO is not allowed. */ + if (new_model == RISCV_MEMORY_CONSISTENCY_MODEL_WMO) + return -EINVAL; + + /* Set the new model in the task struct. */ + set_memory_consitency_model(current, new_model); + + /* + * We need to reschedule all threads of the current process. + * Let's do this by rescheduling all CPUs. + * This is stricter than necessary, but since this call is + * not expected to happen frequently the impact is low. + */ + for_each_cpu(cpu, cpu_online_mask) + smp_send_reschedule(cpu); + + return 0; +} + +int dtso_get_memory_consistency_model(void) +{ + unsigned long cur_model = get_memory_consistency_model(current); + + if (cur_model == RISCV_MEMORY_CONSISTENCY_MODEL_TSO) + return PR_MEMORY_CONSISTENCY_MODEL_RISCV_TSO; + + return PR_MEMORY_CONSISTENCY_MODEL_RISCV_WMO; +} diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index 579662731eaa..20264bdc3092 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -308,5 +308,7 @@ struct prctl_mm_map {
#define PR_SET_MEMORY_CONSISTENCY_MODEL 71 #define PR_GET_MEMORY_CONSISTENCY_MODEL 72 +# define PR_MEMORY_CONSISTENCY_MODEL_RISCV_WMO 1 +# define PR_MEMORY_CONSISTENCY_MODEL_RISCV_TSO 2
#endif /* _LINUX_PRCTL_H */