[PATCH v4 01/12] riscv: Add support for kernel mode vector

Heiko Stuebner
2023-07-11T15:39:19Z

From: Greentime Hu <greentime.hu@sifive.com>

Add kernel_rvv_begin() and kernel_rvv_end() function declarations
and corresponding definitions in kernel_mode_vector.c

These are needed to wrap uses of vector in kernel mode.

Co-developed-by: Vincent Chen <vincent.chen@sifive.com>
Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
---
arch/riscv/include/asm/vector.h | 17 ++++
arch/riscv/kernel/Makefile | 1 +
arch/riscv/kernel/kernel_mode_vector.c | 132 +++++++++++++++++++++++++
3 files changed, 150 insertions(+)
create mode 100644 arch/riscv/kernel/kernel_mode_vector.c

diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
index 3d78930cab51..ac2c23045eec 100644
--- a/arch/riscv/include/asm/vector.h
+++ b/arch/riscv/include/asm/vector.h
@@ -196,6 +196,23 @@ static inline void __switch_to_vector(struct task_struct *prev,
void riscv_v_vstate_ctrl_init(struct task_struct *tsk);
bool riscv_v_vstate_ctrl_user_allowed(void);

+static inline void riscv_v_flush_cpu_state(void)
+{
+ asm volatile (
+ ".option push\n\t"
+ ".option arch, +v\n\t"
+ "vsetvli t0, x0, e8, m8, ta, ma\n\t"
+ "vmv.v.i v0, 0\n\t"
+ "vmv.v.i v8, 0\n\t"
+ "vmv.v.i v16, 0\n\t"
+ "vmv.v.i v24, 0\n\t"
+ ".option pop\n\t"
+ : : : "t0");
+}
+
+void kernel_rvv_begin(void);
+void kernel_rvv_end(void);
+
#else /* ! CONFIG_RISCV_ISA_V */

struct pt_regs;
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 506cc4a9a45a..3f4435746af7 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -61,6 +61,7 @@ obj-$(CONFIG_MMU) += vdso.o vdso/
obj-$(CONFIG_RISCV_M_MODE) += 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_SMP) += smpboot.o
obj-$(CONFIG_SMP) += smp.o
obj-$(CONFIG_SMP) += cpu_ops.o
diff --git a/arch/riscv/kernel/kernel_mode_vector.c b/arch/riscv/kernel/kernel_mode_vector.c
new file mode 100644
index 000000000000..2d704190c054
--- /dev/null
+++ b/arch/riscv/kernel/kernel_mode_vector.c
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Catalin Marinas <catalin.marinas@arm.com>
+ * Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
+ * Copyright (C) 2021 SiFive
+ */
+#include <linux/compiler.h>
+#include <linux/irqflags.h>
+#include <linux/percpu.h>
+#include <linux/preempt.h>
+#include <linux/types.h>
+
+#include <asm/vector.h>
+#include <asm/switch_to.h>
+
+DECLARE_PER_CPU(bool, vector_context_busy);
+DEFINE_PER_CPU(bool, vector_context_busy);
+
+/*
+ * may_use_vector - whether it is allowable at this time to issue vector
+ * instructions or access the vector register file
+ *
+ * Callers must not assume that the result remains true beyond the next
+ * preempt_enable() or return from softirq context.
+ */
+static __must_check inline bool may_use_vector(void)
+{
+ /*
+ * vector_context_busy is only set while preemption is disabled,
+ * and is clear whenever preemption is enabled. Since
+ * this_cpu_read() is atomic w.r.t. preemption, vector_context_busy
+ * cannot change under our feet -- if it's set we cannot be
+ * migrated, and if it's clear we cannot be migrated to a CPU
+ * where it is set.
+ */
+ return !in_irq() && !irqs_disabled() && !in_nmi() &&
+ !this_cpu_read(vector_context_busy);
+}
+
+/*
+ * Claim ownership of the CPU vector context for use by the calling context.
+ *
+ * The caller may freely manipulate the vector context metadata until
+ * put_cpu_vector_context() is called.
+ */
+static void get_cpu_vector_context(void)
+{
+ bool busy;
+
+ preempt_disable();
+ busy = __this_cpu_xchg(vector_context_busy, true);
+
+ WARN_ON(busy);
+}
+
+/*
+ * Release the CPU vector context.
+ *
+ * Must be called from a context in which get_cpu_vector_context() was
+ * previously called, with no call to put_cpu_vector_context() in the
+ * meantime.
+ */
+static void put_cpu_vector_context(void)
+{
+ bool busy = __this_cpu_xchg(vector_context_busy, false);
+
+ WARN_ON(!busy);
+ preempt_enable();
+}
+
+/*
+ * kernel_rvv_begin(): obtain the CPU vector registers for use by the calling
+ * context
+ *
+ * Must not be called unless may_use_vector() returns true.
+ * Task context in the vector registers is saved back to memory as necessary.
+ *
+ * A matching call to kernel_rvv_end() must be made before returning from the
+ * calling context.
+ *
+ * The caller may freely use the vector registers until kernel_rvv_end() is
+ * called.
+ */
+void kernel_rvv_begin(void)
+{
+ if (WARN_ON(!has_vector()))
+ return;
+
+ WARN_ON(!may_use_vector());
+
+ /* Acquire kernel mode vector */
+ get_cpu_vector_context();
+
+ /* Save vector state, if any */
+ riscv_v_vstate_save(current, task_pt_regs(current));
+
+ /* Enable vector */
+ riscv_v_enable();
+
+ /* Invalidate vector regs */
+ riscv_v_flush_cpu_state();
+}
+EXPORT_SYMBOL_GPL(kernel_rvv_begin);
+
+/*
+ * kernel_rvv_end(): give the CPU vector registers back to the current task
+ *
+ * Must be called from a context in which kernel_rvv_begin() was previously
+ * called, with no call to kernel_rvv_end() in the meantime.
+ *
+ * The caller must not use the vector registers after this function is called,
+ * unless kernel_rvv_begin() is called again in the meantime.
+ */
+void kernel_rvv_end(void)
+{
+ if (WARN_ON(!has_vector()))
+ return;
+
+ /* Invalidate vector regs */
+ riscv_v_flush_cpu_state();
+
+ /* Restore vector state, if any */
+ riscv_v_vstate_restore(current, task_pt_regs(current));
+
+ /* disable vector */
+ riscv_v_disable();
+
+ /* release kernel mode vector */
+ put_cpu_vector_context();
+}
+EXPORT_SYMBOL_GPL(kernel_rvv_end);
--
2.39.2