linux/arch/riscv/kernel/kernel_mode_vector.c

// 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 <linux/kvm_types.h>

#include <asm/vector.h>
#include <asm/kvm_vcpu_vector.h>
#include <asm/switch_to.h>
#include <asm/simd.h>
#ifdef CONFIG_RISCV_ISA_V_PREEMPTIVE
#include <asm/asm-prototypes.h>
#endif

static void (* __rcu kvm_flush_vector_ctx_callback)(void);

void kvm_riscv_register_vctx_callback(void (*func)(void))
{
	if (WARN_ON_ONCE(rcu_access_pointer(kvm_flush_vector_ctx_callback)))
		return;

	rcu_assign_pointer(kvm_flush_vector_ctx_callback, func);
}
EXPORT_SYMBOL_GPL(kvm_riscv_register_vctx_callback);

void kvm_riscv_unregister_vctx_callback(void)
{
	rcu_assign_pointer(kvm_flush_vector_ctx_callback, NULL);
	synchronize_rcu();
}
EXPORT_SYMBOL_GPL(kvm_riscv_unregister_vctx_callback);


static inline void riscv_v_start(u32 flags)
{
	int orig;

	orig = riscv_v_flags();
	BUG_ON((orig & flags) != 0);
	riscv_v_flags_set(orig | flags);
	barrier();
}

static inline void riscv_v_stop(u32 flags)
{
	int orig;

	barrier();
	orig = riscv_v_flags();
	BUG_ON((orig & flags) == 0);
	riscv_v_flags_set(orig & ~flags);
}

/*
 * 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.
 */
void get_cpu_vector_context(void)
{
	/*
	 * disable softirqs so it is impossible for softirqs to nest
	 * get_cpu_vector_context() when kernel is actively using Vector.
	 */
	if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
		if (!irqs_disabled())
			local_bh_disable();
	} else {
		preempt_disable();
	}

	riscv_v_start(RISCV_KERNEL_MODE_V);
}
EXPORT_SYMBOL_FOR_KVM(get_cpu_vector_context);

/*
 * 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.
 */
void put_cpu_vector_context(void)
{
	riscv_v_stop(RISCV_KERNEL_MODE_V);

	if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
		if (!irqs_disabled())
			local_bh_enable();
	} else {
		preempt_enable();
	}
}
EXPORT_SYMBOL_FOR_KVM(put_cpu_vector_context);

static void __riscv_flush_vector_context(void)
{
	void (*vcpu_flush_v_callback)(void);

	if (riscv_v_flags() & RISCV_V_VCPU_CTX) {
		rcu_read_lock();
		vcpu_flush_v_callback = rcu_dereference(kvm_flush_vector_ctx_callback);
		vcpu_flush_v_callback();
		rcu_read_unlock();
		return;
	}

	riscv_v_vstate_save(&current->thread.vstate, task_pt_regs(current));
	riscv_v_vstate_set_restore(current, task_pt_regs(current));
}

#ifdef CONFIG_RISCV_ISA_V_PREEMPTIVE
static __always_inline u32 *riscv_v_flags_ptr(void)
{
	return &current->thread.riscv_v_flags;
}

static inline void riscv_preempt_v_set_dirty(void)
{
	*riscv_v_flags_ptr() |= RISCV_PREEMPT_V_DIRTY;
}

static inline void riscv_preempt_v_reset_flags(void)
{
	*riscv_v_flags_ptr() &= ~(RISCV_PREEMPT_V_DIRTY | RISCV_PREEMPT_V_NEED_RESTORE);
}

static inline void riscv_v_ctx_depth_inc(void)
{
	*riscv_v_flags_ptr() += RISCV_V_CTX_UNIT_DEPTH;
}

static inline void riscv_v_ctx_depth_dec(void)
{
	*riscv_v_flags_ptr() -= RISCV_V_CTX_UNIT_DEPTH;
}

static inline u32 riscv_v_ctx_get_depth(void)
{
	return *riscv_v_flags_ptr() & RISCV_V_CTX_DEPTH_MASK;
}

static int riscv_v_stop_kernel_context(void)
{
	if (riscv_v_ctx_get_depth() != 0 || !riscv_preempt_v_started(current))
		return 1;

	riscv_preempt_v_clear_dirty(current);
	riscv_v_stop(RISCV_PREEMPT_V);
	return 0;
}

static int riscv_v_start_kernel_context(void)
{
	struct __riscv_v_ext_state *kvstate;

	kvstate = &current->thread.kernel_vstate;
	if (!kvstate->datap)
		return -ENOENT;

	if (riscv_preempt_v_started(current)) {
		WARN_ON(riscv_v_ctx_get_depth() == 0);
		get_cpu_vector_context();
		if (riscv_preempt_v_dirty(current)) {
			__riscv_v_vstate_save(kvstate, kvstate->datap);
			riscv_preempt_v_clear_dirty(current);
		}
		riscv_preempt_v_set_restore(current);
		return 0;
	}

	/* Transfer the ownership of V from user to kernel, then save */
	get_cpu_vector_context();
	__riscv_flush_vector_context();
	put_cpu_vector_context();
	/*
	 *  A voluntary context switch caused by put_cpu_vector_context() can
	 *  raise the NEED_RESTORE flag if preempt_v starts too early due to a
	 *  failed risv_v_is_on() check.
	 *
	 *  This causes the next context_nesting_end pollute the v-reg from
	 *  the stale context memory in kernel-mode vector.
	 */
	riscv_v_start(RISCV_PREEMPT_V);
	return 0;
}

/* low-level V context handling code, called with irq disabled */
asmlinkage void riscv_v_context_nesting_start(struct pt_regs *regs)
{
	int depth;

	if (!riscv_preempt_v_started(current))
		return;

	depth = riscv_v_ctx_get_depth();
	if (depth == 0 && __riscv_v_vstate_check(regs->status, DIRTY))
		riscv_preempt_v_set_dirty();

	riscv_v_ctx_depth_inc();
}

asmlinkage void riscv_v_context_nesting_end(struct pt_regs *regs)
{
	struct __riscv_v_ext_state *vstate = &current->thread.kernel_vstate;
	u32 depth;

	WARN_ON(!irqs_disabled());

	if (!riscv_preempt_v_started(current))
		return;

	riscv_v_ctx_depth_dec();
	depth = riscv_v_ctx_get_depth();
	if (depth == 0) {
		if (riscv_preempt_v_restore(current)) {
			__riscv_v_vstate_restore(vstate, vstate->datap);
			__riscv_v_vstate_clean(regs);
			riscv_preempt_v_reset_flags();
		}
	}
}
#else
#define riscv_v_start_kernel_context()		(-ENOENT)
#define riscv_v_stop_kernel_context()		(-ENOENT)
#endif /* CONFIG_RISCV_ISA_V_PREEMPTIVE */

/*
 * 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() || has_xtheadvector())))
		return;

	BUG_ON(!may_use_simd());

	if (riscv_v_start_kernel_context()) {
		get_cpu_vector_context();
		__riscv_flush_vector_context();
	}

	riscv_v_enable();
}
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() || has_xtheadvector())))
		return;

	riscv_v_disable();

	if (riscv_v_stop_kernel_context())
		put_cpu_vector_context();
}
EXPORT_SYMBOL_GPL(kernel_vector_end);