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Message-Id: <20230912115728.172982-3-bjorn@kernel.org>
Date: Tue, 12 Sep 2023 13:57:24 +0200
From: Björn Töpel <bjorn@...nel.org>
To: Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
linux-riscv@...ts.infradead.org, Andy Chiu <andy.chiu@...ive.com>,
Greentime Hu <greentime.hu@...ive.com>,
"Jason A . Donenfeld" <Jason@...c4.com>,
Samuel Neves <sneves@....uc.pt>
Cc: Heiko Stuebner <heiko@...ech.de>,
Herbert Xu <herbert@...dor.apana.org.au>,
"David S. Miller" <davem@...emloft.net>,
linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
Vincent Chen <vincent.chen@...ive.com>
Subject: [RFC PATCH 2/6] riscv: Add support for kernel mode vector
From: Greentime Hu <greentime.hu@...ive.com>
Add kernel_vector_begin() and kernel_vector_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@...ive.com>
Signed-off-by: Vincent Chen <vincent.chen@...ive.com>
Signed-off-by: Greentime Hu <greentime.hu@...ive.com>
Signed-off-by: Andy Chiu <andy.chiu@...ive.com>
---
arch/riscv/include/asm/simd.h | 50 ++++++++++++
arch/riscv/include/asm/vector.h | 2 +
arch/riscv/kernel/Makefile | 1 +
arch/riscv/kernel/kernel_mode_vector.c | 101 +++++++++++++++++++++++++
4 files changed, 154 insertions(+)
create mode 100644 arch/riscv/include/asm/simd.h
create mode 100644 arch/riscv/kernel/kernel_mode_vector.c
diff --git a/arch/riscv/include/asm/simd.h b/arch/riscv/include/asm/simd.h
new file mode 100644
index 000000000000..ef70af78005d
--- /dev/null
+++ b/arch/riscv/include/asm/simd.h
@@ -0,0 +1,50 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@...aro.org>
+ * Copyright (C) 2023 SiFive
+ */
+
+#ifndef __ASM_SIMD_H
+#define __ASM_SIMD_H
+
+#include <linux/compiler.h>
+#include <linux/irqflags.h>
+#include <linux/percpu.h>
+#include <linux/preempt.h>
+#include <linux/types.h>
+
+#ifdef CONFIG_RISCV_ISA_V
+
+DECLARE_PER_CPU(bool, vector_context_busy);
+
+/*
+ * may_use_simd - 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_simd(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);
+}
+
+#else /* ! CONFIG_RISCV_ISA_V */
+
+static __must_check inline bool may_use_simd(void)
+{
+ return false;
+}
+
+#endif /* ! CONFIG_RISCV_ISA_V */
+
+#endif
diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
index 531873986a15..768acd517414 100644
--- a/arch/riscv/include/asm/vector.h
+++ b/arch/riscv/include/asm/vector.h
@@ -22,6 +22,8 @@
extern unsigned long riscv_v_vsize;
int riscv_v_setup_vsize(void);
bool riscv_v_first_use_handler(struct pt_regs *regs);
+void kernel_vector_begin(void);
+void kernel_vector_end(void);
static __always_inline bool has_vector(void)
{
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 95cf25d48405..0597bb668b6e 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -62,6 +62,7 @@ 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..1c3b32d2b340
--- /dev/null
+++ b/arch/riscv/kernel/kernel_mode_vector.c
@@ -0,0 +1,101 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Catalin Marinas <catalin.marinas@....com>
+ * Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@...aro.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>
+#include <asm/simd.h>
+
+DEFINE_PER_CPU(bool, 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_vector_begin(): obtain the CPU vector registers for use by the calling
+ * context
+ *
+ * Must not be called unless may_use_simd() returns true.
+ * Task context in the vector registers is saved back to memory as necessary.
+ *
+ * A matching call to kernel_vector_end() must be made before returning from the
+ * calling context.
+ *
+ * The caller may freely use the vector registers until kernel_vector_end() is
+ * called.
+ */
+void kernel_vector_begin(void)
+{
+ if (WARN_ON(!has_vector()))
+ return;
+
+ BUG_ON(!may_use_simd());
+
+ riscv_v_vstate_save(current, task_pt_regs(current));
+
+ get_cpu_vector_context();
+
+ riscv_v_enable();
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(kernel_vector_begin);
+
+/*
+ * kernel_vector_end(): give the CPU vector registers back to the current task
+ *
+ * Must be called from a context in which kernel_vector_begin() was previously
+ * called, with no call to kernel_vector_end() in the meantime.
+ *
+ * The caller must not use the vector registers after this function is called,
+ * unless kernel_vector_begin() is called again in the meantime.
+ */
+void kernel_vector_end(void)
+{
+ if (WARN_ON(!has_vector()))
+ return;
+
+ riscv_v_vstate_set_restore(current, task_pt_regs(current));
+
+ riscv_v_disable();
+
+ put_cpu_vector_context();
+}
+EXPORT_SYMBOL_GPL(kernel_vector_end);
--
2.39.2
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