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linux/arch/riscv/kvm/vcpu_timer.c
Rajnesh Kanwal 6eff380489 riscv/kvm: Fix VM hang in case of timer delta being zero. 
In case when VCPU is blocked due to WFI, we schedule the timer
from `kvm_riscv_vcpu_timer_blocking()` to keep timer interrupt
ticking.

But in case when delta_ns comes to be zero, we never schedule
the timer and VCPU keeps sleeping indefinitely until any activity
is done with VM console.

This is easily reproduce-able using kvmtool.
./lkvm-static run -c1 --console virtio -p "earlycon root=/dev/vda" \
         -k ./Image -d rootfs.ext4

Also, just add a print in kvm_riscv_vcpu_vstimer_expired() to
check the interrupt delivery and run `top` or similar auto-upating
cmd from guest. Within sometime one can notice that print from
timer expiry routine stops and the `top` cmd output will stop
updating.

This change fixes this by making sure we schedule the timer even
with delta_ns being zero to bring the VCPU out of sleep immediately.

Fixes: 8f5cb44b1b ("RISC-V: KVM: Support sstc extension")
Signed-off-by: Rajnesh Kanwal <rkanwal@rivosinc.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Anup Patel <anup@brainfault.org>
2023-03-17 13:32:54 +05:30

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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2019 Western Digital Corporation or its affiliates.
*
* Authors:
* Atish Patra <atish.patra@wdc.com>
*/
#include <linux/errno.h>
#include <linux/err.h>
#include <linux/kvm_host.h>
#include <linux/uaccess.h>
#include <clocksource/timer-riscv.h>
#include <asm/csr.h>
#include <asm/delay.h>
#include <asm/kvm_vcpu_timer.h>
static u64 kvm_riscv_current_cycles(struct kvm_guest_timer *gt)
{
return get_cycles64() + gt->time_delta;
}
static u64 kvm_riscv_delta_cycles2ns(u64 cycles,
struct kvm_guest_timer *gt,
struct kvm_vcpu_timer *t)
{
unsigned long flags;
u64 cycles_now, cycles_delta, delta_ns;
local_irq_save(flags);
cycles_now = kvm_riscv_current_cycles(gt);
if (cycles_now < cycles)
cycles_delta = cycles - cycles_now;
else
cycles_delta = 0;
delta_ns = (cycles_delta * gt->nsec_mult) >> gt->nsec_shift;
local_irq_restore(flags);
return delta_ns;
}
static enum hrtimer_restart kvm_riscv_vcpu_hrtimer_expired(struct hrtimer *h)
{
u64 delta_ns;
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);
struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
if (kvm_riscv_current_cycles(gt) < t->next_cycles) {
delta_ns = kvm_riscv_delta_cycles2ns(t->next_cycles, gt, t);
hrtimer_forward_now(&t->hrt, ktime_set(0, delta_ns));
return HRTIMER_RESTART;
}
t->next_set = false;
kvm_riscv_vcpu_set_interrupt(vcpu, IRQ_VS_TIMER);
return HRTIMER_NORESTART;
}
static int kvm_riscv_vcpu_timer_cancel(struct kvm_vcpu_timer *t)
{
if (!t->init_done || !t->next_set)
return -EINVAL;
hrtimer_cancel(&t->hrt);
t->next_set = false;
return 0;
}
static int kvm_riscv_vcpu_update_vstimecmp(struct kvm_vcpu *vcpu, u64 ncycles)
{
#if defined(CONFIG_32BIT)
csr_write(CSR_VSTIMECMP, ncycles & 0xFFFFFFFF);
csr_write(CSR_VSTIMECMPH, ncycles >> 32);
#else
csr_write(CSR_VSTIMECMP, ncycles);
#endif
return 0;
}
static int kvm_riscv_vcpu_update_hrtimer(struct kvm_vcpu *vcpu, u64 ncycles)
{
struct kvm_vcpu_timer *t = &vcpu->arch.timer;
struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
u64 delta_ns;
if (!t->init_done)
return -EINVAL;
kvm_riscv_vcpu_unset_interrupt(vcpu, IRQ_VS_TIMER);
delta_ns = kvm_riscv_delta_cycles2ns(ncycles, gt, t);
t->next_cycles = ncycles;
hrtimer_start(&t->hrt, ktime_set(0, delta_ns), HRTIMER_MODE_REL);
t->next_set = true;
return 0;
}
int kvm_riscv_vcpu_timer_next_event(struct kvm_vcpu *vcpu, u64 ncycles)
{
struct kvm_vcpu_timer *t = &vcpu->arch.timer;
return t->timer_next_event(vcpu, ncycles);
}
static enum hrtimer_restart kvm_riscv_vcpu_vstimer_expired(struct hrtimer *h)
{
u64 delta_ns;
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);
struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
if (kvm_riscv_current_cycles(gt) < t->next_cycles) {
delta_ns = kvm_riscv_delta_cycles2ns(t->next_cycles, gt, t);
hrtimer_forward_now(&t->hrt, ktime_set(0, delta_ns));
return HRTIMER_RESTART;
}
t->next_set = false;
kvm_vcpu_kick(vcpu);
return HRTIMER_NORESTART;
}
bool kvm_riscv_vcpu_timer_pending(struct kvm_vcpu *vcpu)
{
struct kvm_vcpu_timer *t = &vcpu->arch.timer;
struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
if (!kvm_riscv_delta_cycles2ns(t->next_cycles, gt, t) ||
kvm_riscv_vcpu_has_interrupts(vcpu, 1UL << IRQ_VS_TIMER))
return true;
else
return false;
}
static void kvm_riscv_vcpu_timer_blocking(struct kvm_vcpu *vcpu)
{
struct kvm_vcpu_timer *t = &vcpu->arch.timer;
struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
u64 delta_ns;
if (!t->init_done)
return;
delta_ns = kvm_riscv_delta_cycles2ns(t->next_cycles, gt, t);
hrtimer_start(&t->hrt, ktime_set(0, delta_ns), HRTIMER_MODE_REL);
t->next_set = true;
}
static void kvm_riscv_vcpu_timer_unblocking(struct kvm_vcpu *vcpu)
{
kvm_riscv_vcpu_timer_cancel(&vcpu->arch.timer);
}
int kvm_riscv_vcpu_get_reg_timer(struct kvm_vcpu *vcpu,
const struct kvm_one_reg *reg)
{
struct kvm_vcpu_timer *t = &vcpu->arch.timer;
struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
u64 __user *uaddr = (u64 __user *)(unsigned long)reg->addr;
unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
KVM_REG_SIZE_MASK |
KVM_REG_RISCV_TIMER);
u64 reg_val;
if (KVM_REG_SIZE(reg->id) != sizeof(u64))
return -EINVAL;
if (reg_num >= sizeof(struct kvm_riscv_timer) / sizeof(u64))
return -EINVAL;
switch (reg_num) {
case KVM_REG_RISCV_TIMER_REG(frequency):
reg_val = riscv_timebase;
break;
case KVM_REG_RISCV_TIMER_REG(time):
reg_val = kvm_riscv_current_cycles(gt);
break;
case KVM_REG_RISCV_TIMER_REG(compare):
reg_val = t->next_cycles;
break;
case KVM_REG_RISCV_TIMER_REG(state):
reg_val = (t->next_set) ? KVM_RISCV_TIMER_STATE_ON :
KVM_RISCV_TIMER_STATE_OFF;
break;
default:
return -EINVAL;
}
if (copy_to_user(uaddr, &reg_val, KVM_REG_SIZE(reg->id)))
return -EFAULT;
return 0;
}
int kvm_riscv_vcpu_set_reg_timer(struct kvm_vcpu *vcpu,
const struct kvm_one_reg *reg)
{
struct kvm_vcpu_timer *t = &vcpu->arch.timer;
struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
u64 __user *uaddr = (u64 __user *)(unsigned long)reg->addr;
unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
KVM_REG_SIZE_MASK |
KVM_REG_RISCV_TIMER);
u64 reg_val;
int ret = 0;
if (KVM_REG_SIZE(reg->id) != sizeof(u64))
return -EINVAL;
if (reg_num >= sizeof(struct kvm_riscv_timer) / sizeof(u64))
return -EINVAL;
if (copy_from_user(&reg_val, uaddr, KVM_REG_SIZE(reg->id)))
return -EFAULT;
switch (reg_num) {
case KVM_REG_RISCV_TIMER_REG(frequency):
ret = -EOPNOTSUPP;
break;
case KVM_REG_RISCV_TIMER_REG(time):
gt->time_delta = reg_val - get_cycles64();
break;
case KVM_REG_RISCV_TIMER_REG(compare):
t->next_cycles = reg_val;
break;
case KVM_REG_RISCV_TIMER_REG(state):
if (reg_val == KVM_RISCV_TIMER_STATE_ON)
ret = kvm_riscv_vcpu_timer_next_event(vcpu, reg_val);
else
ret = kvm_riscv_vcpu_timer_cancel(t);
break;
default:
ret = -EINVAL;
break;
}
return ret;
}
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_REL);
t->init_done = true;
t->next_set = false;
/* Enable sstc for every vcpu if available in hardware */
if (riscv_isa_extension_available(NULL, SSTC)) {
t->sstc_enabled = true;
t->hrt.function = kvm_riscv_vcpu_vstimer_expired;
t->timer_next_event = kvm_riscv_vcpu_update_vstimecmp;
} else {
t->sstc_enabled = false;
t->hrt.function = kvm_riscv_vcpu_hrtimer_expired;
t->timer_next_event = kvm_riscv_vcpu_update_hrtimer;
}
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)
{
struct kvm_vcpu_timer *t = &vcpu->arch.timer;
t->next_cycles = -1ULL;
return kvm_riscv_vcpu_timer_cancel(&vcpu->arch.timer);
}
static void kvm_riscv_vcpu_update_timedelta(struct kvm_vcpu *vcpu)
{
struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
#if defined(CONFIG_32BIT)
csr_write(CSR_HTIMEDELTA, (u32)(gt->time_delta));
csr_write(CSR_HTIMEDELTAH, (u32)(gt->time_delta >> 32));
#else
csr_write(CSR_HTIMEDELTA, gt->time_delta);
#endif
}
void kvm_riscv_vcpu_timer_restore(struct kvm_vcpu *vcpu)
{
struct kvm_vcpu_timer *t = &vcpu->arch.timer;
kvm_riscv_vcpu_update_timedelta(vcpu);
if (!t->sstc_enabled)
return;
#if defined(CONFIG_32BIT)
csr_write(CSR_VSTIMECMP, (u32)t->next_cycles);
csr_write(CSR_VSTIMECMPH, (u32)(t->next_cycles >> 32));
#else
csr_write(CSR_VSTIMECMP, t->next_cycles);
#endif
/* timer should be enabled for the remaining operations */
if (unlikely(!t->init_done))
return;
kvm_riscv_vcpu_timer_unblocking(vcpu);
}
void kvm_riscv_vcpu_timer_sync(struct kvm_vcpu *vcpu)
{
struct kvm_vcpu_timer *t = &vcpu->arch.timer;
if (!t->sstc_enabled)
return;
#if defined(CONFIG_32BIT)
t->next_cycles = csr_read(CSR_VSTIMECMP);
t->next_cycles |= (u64)csr_read(CSR_VSTIMECMPH) << 32;
#else
t->next_cycles = csr_read(CSR_VSTIMECMP);
#endif
}
void kvm_riscv_vcpu_timer_save(struct kvm_vcpu *vcpu)
{
struct kvm_vcpu_timer *t = &vcpu->arch.timer;
if (!t->sstc_enabled)
return;
/*
* The vstimecmp CSRs are saved by kvm_riscv_vcpu_timer_sync()
* upon every VM exit so no need to save here.
*/
/* timer should be enabled for the remaining operations */
if (unlikely(!t->init_done))
return;
if (kvm_vcpu_is_blocking(vcpu))
kvm_riscv_vcpu_timer_blocking(vcpu);
}
void kvm_riscv_guest_timer_init(struct kvm *kvm)
{
struct kvm_guest_timer *gt = &kvm->arch.timer;
riscv_cs_get_mult_shift(&gt->nsec_mult, &gt->nsec_shift);
gt->time_delta = -get_cycles64();
}
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