[PATCH v4 15/20] RISC-V: KVM: Add timer functionality

[Anup Patel]

From: Atish Patra <atish.patra@xxxxxxx>

The RISC-V hypervisor specification doesn't have any virtual timer
feature.

Due to this, the guest VCPU timer will be programmed via SBI calls.
The host will use a separate hrtimer event for each guest VCPU to
provide timer functionality. We inject a virtual timer interrupt to
the guest VCPU whenever the guest VCPU hrtimer event expires.

The following features are not supported yet and will be added in
future:
1. A time offset to adjust guest time from host time
2. A saved next event in guest vcpu for vm migration

Signed-off-by: Atish Patra <atish.patra@xxxxxxx>
Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
---
 arch/riscv/include/asm/kvm_host.h       |   4 +
 arch/riscv/include/asm/kvm_vcpu_timer.h |  32 +++++++
 arch/riscv/kvm/Makefile                 |   2 +-
 arch/riscv/kvm/vcpu.c                   |   6 ++
 arch/riscv/kvm/vcpu_timer.c             | 106 ++++++++++++++++++++++++
 drivers/clocksource/timer-riscv.c       |   8 ++
 include/clocksource/timer-riscv.h       |  16 ++++
 7 files changed, 173 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/include/asm/kvm_vcpu_timer.h
 create mode 100644 arch/riscv/kvm/vcpu_timer.c
 create mode 100644 include/clocksource/timer-riscv.h

diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
index ab33e59a3d88..d2a2e45eefc0 100644
--- a/arch/riscv/include/asm/kvm_host.h
+++ b/arch/riscv/include/asm/kvm_host.h
@@ -12,6 +12,7 @@
 #include <linux/types.h>
 #include <linux/kvm.h>
 #include <linux/kvm_types.h>
+#include <asm/kvm_vcpu_timer.h>
 
 #ifdef CONFIG_64BIT
 #define KVM_MAX_VCPUS			(1U << 16)
@@ -167,6 +168,9 @@ struct kvm_vcpu_arch {
 	unsigned long irqs_pending;
 	unsigned long irqs_pending_mask;
 
+	/* VCPU Timer */
+	struct kvm_vcpu_timer timer;
+
 	/* MMIO instruction details */
 	struct kvm_mmio_decode mmio_decode;
 
diff --git a/arch/riscv/include/asm/kvm_vcpu_timer.h b/arch/riscv/include/asm/kvm_vcpu_timer.h
new file mode 100644
index 000000000000..df67ea86988e
--- /dev/null
+++ b/arch/riscv/include/asm/kvm_vcpu_timer.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2019 Western Digital Corporation or its affiliates.
+ *
+ * Authors:
+ *	Atish Patra <atish.patra@xxxxxxx>
+ */
+
+#ifndef __KVM_VCPU_RISCV_TIMER_H
+#define __KVM_VCPU_RISCV_TIMER_H
+
+#include <linux/hrtimer.h>
+
+#define VCPU_TIMER_PROGRAM_THRESHOLD_NS		1000
+
+struct kvm_vcpu_timer {
+	bool init_done;
+	/* Check if the timer is programmed */
+	bool is_set;
+	struct hrtimer hrt;
+	/* Mult & Shift values to get nanosec from cycles */
+	u32 mult;
+	u32 shift;
+};
+
+int kvm_riscv_vcpu_timer_init(struct kvm_vcpu *vcpu);
+int kvm_riscv_vcpu_timer_deinit(struct kvm_vcpu *vcpu);
+int kvm_riscv_vcpu_timer_reset(struct kvm_vcpu *vcpu);
+int kvm_riscv_vcpu_timer_next_event(struct kvm_vcpu *vcpu,
+				    unsigned long ncycles);
+
+#endif
diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
index c0f57f26c13d..3e0c7558320d 100644
--- a/arch/riscv/kvm/Makefile
+++ b/arch/riscv/kvm/Makefile
@@ -9,6 +9,6 @@ ccflags-y := -Ivirt/kvm -Iarch/riscv/kvm
 kvm-objs := $(common-objs-y)
 
 kvm-objs += main.o vm.o vmid.o tlb.o mmu.o
-kvm-objs += vcpu.o vcpu_exit.o vcpu_switch.o
+kvm-objs += vcpu.o vcpu_exit.o vcpu_switch.o vcpu_timer.o
 
 obj-$(CONFIG_KVM)	+= kvm.o
diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index 6124077d154f..018fca436776 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -54,6 +54,8 @@ static void kvm_riscv_reset_vcpu(struct kvm_vcpu *vcpu)
 
 	memcpy(cntx, reset_cntx, sizeof(*cntx));
 
+	kvm_riscv_vcpu_timer_reset(vcpu);
+
 	WRITE_ONCE(vcpu->arch.irqs_pending, 0);
 	WRITE_ONCE(vcpu->arch.irqs_pending_mask, 0);
 }
@@ -108,6 +110,9 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 	cntx->hstatus |= HSTATUS_SP2P;
 	cntx->hstatus |= HSTATUS_SPV;
 
+	/* Setup VCPU timer */
+	kvm_riscv_vcpu_timer_init(vcpu);
+
 	/* Reset VCPU */
 	kvm_riscv_reset_vcpu(vcpu);
 
@@ -116,6 +121,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 
 void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
 {
+	kvm_riscv_vcpu_timer_deinit(vcpu);
 	kvm_riscv_stage2_flush_cache(vcpu);
 	kmem_cache_free(kvm_vcpu_cache, vcpu);
 }
diff --git a/arch/riscv/kvm/vcpu_timer.c b/arch/riscv/kvm/vcpu_timer.c
new file mode 100644
index 000000000000..a45ca06e1aa6
--- /dev/null
+++ b/arch/riscv/kvm/vcpu_timer.c
@@ -0,0 +1,106 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 Western Digital Corporation or its affiliates.
+ *
+ * Authors:
+ *     Atish Patra <atish.patra@xxxxxxx>
+ */
+
+#include <linux/errno.h>
+#include <linux/err.h>
+#include <linux/kvm_host.h>
+#include <clocksource/timer-riscv.h>
+#include <asm/csr.h>
+#include <asm/kvm_vcpu_timer.h>
+
+static enum hrtimer_restart kvm_riscv_vcpu_hrtimer_expired(struct hrtimer *h)
+{
+	struct kvm_vcpu_timer *t = container_of(h, struct kvm_vcpu_timer, hrt);
+	struct kvm_vcpu *vcpu = container_of(t, struct kvm_vcpu, arch.timer);
+
+	t->is_set = false;
+	kvm_riscv_vcpu_set_interrupt(vcpu, IRQ_S_TIMER);
+
+	return HRTIMER_NORESTART;
+}
+
+static u64 kvm_riscv_delta_cycles2ns(u64 cycles, struct kvm_vcpu_timer *t)
+{
+	unsigned long flags;
+	u64 cycles_now, cycles_delta, delta_ns;
+
+	local_irq_save(flags);
+	cycles_now = get_cycles64();
+	if (cycles_now < cycles)
+		cycles_delta = cycles - cycles_now;
+	else
+		cycles_delta = 0;
+	delta_ns = (cycles_delta * t->mult) >> t->shift;
+	local_irq_restore(flags);
+
+	return delta_ns;
+}
+
+static int kvm_riscv_vcpu_timer_cancel(struct kvm_vcpu_timer *t)
+{
+	if (!t->init_done || !t->is_set)
+		return -EINVAL;
+
+	hrtimer_cancel(&t->hrt);
+	t->is_set = false;
+
+	return 0;
+}
+
+int kvm_riscv_vcpu_timer_next_event(struct kvm_vcpu *vcpu,
+				    unsigned long ncycles)
+{
+	struct kvm_vcpu_timer *t = &vcpu->arch.timer;
+	u64 delta_ns = kvm_riscv_delta_cycles2ns(ncycles, t);
+
+	if (!t->init_done)
+		return -EINVAL;
+
+	kvm_riscv_vcpu_unset_interrupt(vcpu, IRQ_S_TIMER);
+
+	if (delta_ns > VCPU_TIMER_PROGRAM_THRESHOLD_NS) {
+		hrtimer_start(&t->hrt, ktime_add_ns(ktime_get(), delta_ns),
+				HRTIMER_MODE_ABS);
+		t->is_set = true;
+	} else
+		kvm_riscv_vcpu_set_interrupt(vcpu, IRQ_S_TIMER);
+
+	return 0;
+}
+
+int kvm_riscv_vcpu_timer_init(struct kvm_vcpu *vcpu)
+{
+	struct kvm_vcpu_timer *t = &vcpu->arch.timer;
+
+	if (t->init_done)
+		return -EINVAL;
+
+	hrtimer_init(&t->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+	t->hrt.function = kvm_riscv_vcpu_hrtimer_expired;
+	t->init_done = true;
+	t->is_set = false;
+
+	riscv_cs_get_mult_shift(&t->mult, &t->shift);
+
+	return 0;
+}
+
+int kvm_riscv_vcpu_timer_deinit(struct kvm_vcpu *vcpu)
+{
+	int ret;
+
+	ret = kvm_riscv_vcpu_timer_cancel(&vcpu->arch.timer);
+	vcpu->arch.timer.init_done = false;
+
+	return ret;
+}
+
+int kvm_riscv_vcpu_timer_reset(struct kvm_vcpu *vcpu)
+{
+	return kvm_riscv_vcpu_timer_cancel(&vcpu->arch.timer);
+}
diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
index 09e031176bc6..7c595203aa5c 100644
--- a/drivers/clocksource/timer-riscv.c
+++ b/drivers/clocksource/timer-riscv.c
@@ -8,6 +8,7 @@
 #include <linux/cpu.h>
 #include <linux/delay.h>
 #include <linux/irq.h>
+#include <linux/module.h>
 #include <linux/sched_clock.h>
 #include <asm/smp.h>
 #include <asm/sbi.h>
@@ -80,6 +81,13 @@ static int riscv_timer_dying_cpu(unsigned int cpu)
 	return 0;
 }
 
+void riscv_cs_get_mult_shift(u32 *mult, u32 *shift)
+{
+	*mult = riscv_clocksource.mult;
+	*shift = riscv_clocksource.shift;
+}
+EXPORT_SYMBOL_GPL(riscv_cs_get_mult_shift);
+
 /* called directly from the low-level interrupt handler */
 void riscv_timer_interrupt(void)
 {
diff --git a/include/clocksource/timer-riscv.h b/include/clocksource/timer-riscv.h
new file mode 100644
index 000000000000..e94e4feecbe8
--- /dev/null
+++ b/include/clocksource/timer-riscv.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2019 Western Digital Corporation or its affiliates.
+ *
+ * Authors:
+ *	Atish Patra <atish.patra@xxxxxxx>
+ */
+
+#ifndef __TIMER_RISCV_H
+#define __TIMER_RISCV_H
+
+#include <linux/types.h>
+
+void riscv_cs_get_mult_shift(u32 *mult, u32 *shift);
+
+#endif
-- 
2.17.1