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Message-ID: <408e06fe-6c98-129c-d369-ba4e91b07ea6@loongson.cn>
Date: Mon, 4 Dec 2023 16:48:59 +0800
From: zhaotianrui <zhaotianrui@...ngson.cn>
To: Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>
Cc: WANG Xuerui <kernel@...0n.name>, kvm@...r.kernel.org,
loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] LoongArch: KVM: Remove kvm_acquire_timer before
entering guest
Reviewed-by: Tianrui Zhao <zhaotianrui@...ngson.cn>
在 2023/11/16 上午10:30, Bibo Mao 写道:
> Timer emulation method in VM is switch to SW timer, there are two
> places where timer emulation is needed. One is during vcpu thread
> context switch, the other is halt-polling with idle instruction
> emulation. SW timer switching is remove during halt-polling mode,
> so it is not necessary to disable SW timer before entering to guest.
>
> This patch removes SW timer handling before entering guest mode, and
> put it in HW timer restoring flow when vcpu thread is sched-in. With
> this patch, vm timer emulation is simpler, there is SW/HW timer
> switch only in vcpu thread context switch scenario.
>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
> arch/loongarch/include/asm/kvm_vcpu.h | 1 -
> arch/loongarch/kvm/timer.c | 22 ++++++--------------
> arch/loongarch/kvm/vcpu.c | 29 ---------------------------
> 3 files changed, 6 insertions(+), 46 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/kvm_vcpu.h b/arch/loongarch/include/asm/kvm_vcpu.h
> index 553cfa2b2b1c..0e87652f780a 100644
> --- a/arch/loongarch/include/asm/kvm_vcpu.h
> +++ b/arch/loongarch/include/asm/kvm_vcpu.h
> @@ -55,7 +55,6 @@ void kvm_save_fpu(struct loongarch_fpu *fpu);
> void kvm_restore_fpu(struct loongarch_fpu *fpu);
> void kvm_restore_fcsr(struct loongarch_fpu *fpu);
>
> -void kvm_acquire_timer(struct kvm_vcpu *vcpu);
> void kvm_init_timer(struct kvm_vcpu *vcpu, unsigned long hz);
> void kvm_reset_timer(struct kvm_vcpu *vcpu);
> void kvm_save_timer(struct kvm_vcpu *vcpu);
> diff --git a/arch/loongarch/kvm/timer.c b/arch/loongarch/kvm/timer.c
> index e37c0ebffabd..711982f9eeb5 100644
> --- a/arch/loongarch/kvm/timer.c
> +++ b/arch/loongarch/kvm/timer.c
> @@ -64,19 +64,6 @@ void kvm_init_timer(struct kvm_vcpu *vcpu, unsigned long timer_hz)
> kvm_write_sw_gcsr(vcpu->arch.csr, LOONGARCH_CSR_TVAL, 0);
> }
>
> -/*
> - * Restore hard timer state and enable guest to access timer registers
> - * without trap, should be called with irq disabled
> - */
> -void kvm_acquire_timer(struct kvm_vcpu *vcpu)
> -{
> - /*
> - * Freeze the soft-timer and sync the guest stable timer with it. We do
> - * this with interrupts disabled to avoid latency.
> - */
> - hrtimer_cancel(&vcpu->arch.swtimer);
> -}
> -
> /*
> * Restore soft timer state from saved context.
> */
> @@ -98,6 +85,11 @@ void kvm_restore_timer(struct kvm_vcpu *vcpu)
> return;
> }
>
> + /*
> + * Freeze the soft-timer and sync the guest stable timer with it.
> + */
> + hrtimer_cancel(&vcpu->arch.swtimer);
> +
> /*
> * Set remainder tick value if not expired
> */
> @@ -115,7 +107,7 @@ void kvm_restore_timer(struct kvm_vcpu *vcpu)
> /*
> * Inject timer here though sw timer should inject timer
> * interrupt async already, since sw timer may be cancelled
> - * during injecting intr async in function kvm_acquire_timer
> + * during injecting intr async
> */
> kvm_queue_irq(vcpu, INT_TI);
> }
> @@ -140,11 +132,9 @@ static void _kvm_save_timer(struct kvm_vcpu *vcpu)
> vcpu->arch.expire = expire;
> if (ticks) {
> /*
> - * Update hrtimer to use new timeout
> * HRTIMER_MODE_PINNED is suggested since vcpu may run in
> * the same physical cpu in next time
> */
> - hrtimer_cancel(&vcpu->arch.swtimer);
> hrtimer_start(&vcpu->arch.swtimer, expire, HRTIMER_MODE_ABS_PINNED);
> } else if (vcpu->stat.generic.blocking) {
> /*
> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
> index 42663a345bd1..cf1c4d64c1b7 100644
> --- a/arch/loongarch/kvm/vcpu.c
> +++ b/arch/loongarch/kvm/vcpu.c
> @@ -95,7 +95,6 @@ static int kvm_pre_enter_guest(struct kvm_vcpu *vcpu)
> * check vmid before vcpu enter guest
> */
> local_irq_disable();
> - kvm_acquire_timer(vcpu);
> kvm_deliver_intr(vcpu);
> kvm_deliver_exception(vcpu);
> /* Make sure the vcpu mode has been written */
> @@ -251,23 +250,6 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
> return -EINVAL;
> }
>
> -/**
> - * kvm_migrate_count() - Migrate timer.
> - * @vcpu: Virtual CPU.
> - *
> - * Migrate hrtimer to the current CPU by cancelling and restarting it
> - * if the hrtimer is active.
> - *
> - * Must be called when the vCPU is migrated to a different CPU, so that
> - * the timer can interrupt the guest at the new CPU, and the timer irq can
> - * be delivered to the vCPU.
> - */
> -static void kvm_migrate_count(struct kvm_vcpu *vcpu)
> -{
> - if (hrtimer_cancel(&vcpu->arch.swtimer))
> - hrtimer_restart(&vcpu->arch.swtimer);
> -}
> -
> static int _kvm_getcsr(struct kvm_vcpu *vcpu, unsigned int id, u64 *val)
> {
> unsigned long gintc;
> @@ -796,17 +778,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> unsigned long flags;
>
> local_irq_save(flags);
> - if (vcpu->arch.last_sched_cpu != cpu) {
> - kvm_debug("[%d->%d]KVM vCPU[%d] switch\n",
> - vcpu->arch.last_sched_cpu, cpu, vcpu->vcpu_id);
> - /*
> - * Migrate the timer interrupt to the current CPU so that it
> - * always interrupts the guest and synchronously triggers a
> - * guest timer interrupt.
> - */
> - kvm_migrate_count(vcpu);
> - }
> -
> /* Restore guest state to registers */
> _kvm_vcpu_load(vcpu, cpu);
> local_irq_restore(flags);
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