linux-kernel - Re: [PATCH 1/3] KVM: LAPIC: Make lapic timer unpinned when timer is injected by posted-interrupt

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Date:   Thu, 6 Jun 2019 13:44:32 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH 1/3] KVM: LAPIC: Make lapic timer unpinned when timer is
 injected by posted-interrupt

On Wed, 5 Jun 2019 at 21:04, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 05/06/19 12:09, Wanpeng Li wrote:
> > +static inline bool posted_interrupt_inject_timer(struct kvm_vcpu *vcpu)
> > +{
> > +     return (kvm_x86_ops->pi_inject_timer_enabled(vcpu) &&
> > +             kvm_mwait_in_guest(vcpu->kvm));
> > +}
> > +
>
> Here you need to check kvm_halt_in_guest, not kvm_mwait_in_guest,
> because you need to go through kvm_apic_expired if the guest needs to be
> woken up from kvm_vcpu_block.
>
> There is a case when you get to kvm_vcpu_block with kvm_halt_in_guest,
> which is when the guest disables asynchronous page faults.  Currently,
> timer interrupts are delivered while apf.halted = true, with this change

You are right. I check it in v2 2/3.

> they wouldn't.  I would just disable KVM_REQ_APF_HALT in
> kvm_can_do_async_pf if kvm_halt_in_guest is true, let me send a patch
> for that later.
>
> When you do this, I think you don't need the
> kvm_x86_ops->pi_inject_timer_enabled check at all, because if we know

I still keep check mwait and apicv in v2, since w/o mwait exposed, the
emulated timer can't be offload(thanks to preemption timer is
disabled). In addition,  w/o posted-interrupt, we can't avoid the
timer fire vmexit.

> that the vCPU cannot be asleep in kvm_vcpu_block, then we can inject the
> timer interrupt immediately with __apic_accept_irq (if APICv is
> disabled, it will set IRR and do kvm_make_request + kvm_vcpu_kick).
>
> You can keep the module parameter, mostly for debugging reasons, but
> please move it from kvm-intel to kvm, and add something like
>
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index 123ea07a3f3b..1cc7973c382e 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -14,6 +14,11 @@
>  static cpumask_var_t housekeeping_mask;
>  static unsigned int housekeeping_flags;
>
> +bool housekeeping_enabled(enum hk_flags flags)
> +{
> +       return !!(housekeeping_flags & flags);
> +}
> +
>  int housekeeping_any_cpu(enum hk_flags flags)
>  {
>         if (static_branch_unlikely(&housekeeping_overridden))
>
> so that the default for the module parameter can be
> housekeeping_enabled(HK_FLAG_TIMER).

Agreed. Thanks for the quick review. :)

Regards,
Wanpeng Li