linux-kernel - Re: [PATCH v4 1/3] LoongArch: KVM: Remove SW timer switch when vcpu is halt polling

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Message-ID: <17c54ef9-9ce5-bc2b-0566-851fe4da9483@loongson.cn>
Date:   Tue, 5 Dec 2023 11:18:16 +0800
From:   maobibo <maobibo@...ngson.cn>
To:     Huacai Chen <chenhuacai@...nel.org>,
        zhaotianrui <zhaotianrui@...ngson.cn>
Cc:     WANG Xuerui <kernel@...0n.name>, kvm@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] LoongArch: KVM: Remove SW timer switch when vcpu
 is halt polling



On 2023/12/5 上午10:20, Huacai Chen wrote:
> This series looks good to me, If Paolo agrees, I will apply to
> loongarch-next after [1] is taken into the kvm tree (otherwise there
> will be build errors).
> 
> [1] https://lore.kernel.org/loongarch/CAAhV-H63QkfSw+Esn8oW2PDEsCnTRPFqkj8X-x8i9cH3AS0k9w@mail.gmail.com/T/#t
> 
Got it, and thanks for your information.

Regards
Bibo Mao

> On Mon, Dec 4, 2023 at 4:45 PM zhaotianrui <zhaotianrui@...ngson.cn> wrote:
>>
>> Reviewed-by: Tianrui Zhao <zhaotianrui@...ngson.cn>
>>
>> 在 2023/11/16 上午10:30, Bibo Mao 写道:
>>> With halt-polling supported, there is checking for pending events
>>> or interrupts when vcpu executes idle instruction. Pending interrupts
>>> include injected SW interrupts and passthrough HW interrupts, such as
>>> HW timer interrupts, since HW timer works still even if vcpu exists
>>> from VM mode.
>>>
>>> Since HW timer pending interrupt can be set directly with CSR status
>>> register, and pending HW timer interrupt checking is used in vcpu block
>>> checking function, it is not necessary to switch to sw timer during
>>> halt-polling. This patch adds preemption disabling in function
>>> kvm_cpu_has_pending_timer, and removes SW timer switching in idle
>>> instruction emulation function.
>>>
>>> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
>>> ---
>>>    arch/loongarch/kvm/exit.c  | 13 ++-----------
>>>    arch/loongarch/kvm/timer.c | 13 ++++++++++---
>>>    arch/loongarch/kvm/vcpu.c  |  9 ++++++++-
>>>    3 files changed, 20 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
>>> index ce8de3fa472c..e708a1786d6b 100644
>>> --- a/arch/loongarch/kvm/exit.c
>>> +++ b/arch/loongarch/kvm/exit.c
>>> @@ -200,17 +200,8 @@ int kvm_emu_idle(struct kvm_vcpu *vcpu)
>>>        ++vcpu->stat.idle_exits;
>>>        trace_kvm_exit_idle(vcpu, KVM_TRACE_EXIT_IDLE);
>>>
>>> -     if (!kvm_arch_vcpu_runnable(vcpu)) {
>>> -             /*
>>> -              * Switch to the software timer before halt-polling/blocking as
>>> -              * the guest's timer may be a break event for the vCPU, and the
>>> -              * hypervisor timer runs only when the CPU is in guest mode.
>>> -              * Switch before halt-polling so that KVM recognizes an expired
>>> -              * timer before blocking.
>>> -              */
>>> -             kvm_save_timer(vcpu);
>>> -             kvm_vcpu_block(vcpu);
>>> -     }
>>> +     if (!kvm_arch_vcpu_runnable(vcpu))
>>> +             kvm_vcpu_halt(vcpu);
>>>
>>>        return EMULATE_DONE;
>>>    }
>>> diff --git a/arch/loongarch/kvm/timer.c b/arch/loongarch/kvm/timer.c
>>> index 284bf553fefe..437e960d8fdb 100644
>>> --- a/arch/loongarch/kvm/timer.c
>>> +++ b/arch/loongarch/kvm/timer.c
>>> @@ -155,11 +155,18 @@ static void _kvm_save_timer(struct kvm_vcpu *vcpu)
>>>                 */
>>>                hrtimer_cancel(&vcpu->arch.swtimer);
>>>                hrtimer_start(&vcpu->arch.swtimer, expire, HRTIMER_MODE_ABS_PINNED);
>>> -     } else
>>> +     } else if (vcpu->stat.generic.blocking) {
>>>                /*
>>> -              * Inject timer interrupt so that hall polling can dectect and exit
>>> +              * Inject timer interrupt so that hall polling can dectect and
>>> +              * exit.
>>> +              * VCPU is scheduled out already and sleeps in rcuwait queue and
>>> +              * will not poll pending events again. kvm_queue_irq is not
>>> +              * enough, hrtimer swtimer should be used here.
>>>                 */
>>> -             kvm_queue_irq(vcpu, INT_TI);
>>> +             expire = ktime_add_ns(ktime_get(), 10);  // 10ns is enough here?
>>> +             vcpu->arch.expire = expire;
>>> +             hrtimer_start(&vcpu->arch.swtimer, expire, HRTIMER_MODE_ABS_PINNED);
>>> +     }
>>>    }
>>>
>>>    /*
>>> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
>>> index 73d0c2b9c1a5..42663a345bd1 100644
>>> --- a/arch/loongarch/kvm/vcpu.c
>>> +++ b/arch/loongarch/kvm/vcpu.c
>>> @@ -187,8 +187,15 @@ int kvm_arch_vcpu_ioctl_translate(struct kvm_vcpu *vcpu,
>>>
>>>    int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
>>>    {
>>> -     return kvm_pending_timer(vcpu) ||
>>> +     int ret;
>>> +
>>> +     /* protect from TOD sync and vcpu_load/put */
>>> +     preempt_disable();
>>> +     ret = kvm_pending_timer(vcpu) ||
>>>                kvm_read_hw_gcsr(LOONGARCH_CSR_ESTAT) & (1 << INT_TI);
>>> +     preempt_enable();
>>> +
>>> +     return ret;
>>>    }
>>>
>>>    int kvm_arch_vcpu_dump_regs(struct kvm_vcpu *vcpu)
>>
>>