linux-kernel - Re: [PATCH 4/6] kvm: lapic: Add apicv activate/deactivate helper function

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Message-ID: <813c8c15-af74-6d77-4a30-2e0ee4b05006@amazon.de>
Date:   Thu, 9 May 2019 00:27:25 +0200
From:   Jan H. Schönherr <jschoenh@...zon.de>
To:     "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Cc:     "joro@...tes.org" <joro@...tes.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>
Subject: Re: [PATCH 4/6] kvm: lapic: Add apicv activate/deactivate helper
 function

On 22/03/2019 12.57, Suthikulpanit, Suravee wrote:
> Introduce a helper function for setting lapic parameters when
> activate/deactivate apicv.
> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>  arch/x86/kvm/lapic.c | 23 ++++++++++++++++++-----
>  arch/x86/kvm/lapic.h |  1 +
>  2 files changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 95295cf81283..9c5cd1a98928 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2126,6 +2126,22 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
>  
>  }
>  
> +void kvm_apic_update_apicv(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_lapic *apic = vcpu->arch.apic;
> +	bool active = vcpu->arch.apicv_active;
> +
> +	if (active) {
> +		/* irr_pending is always true when apicv is activated. */
> +		apic->irr_pending = true;
> +		apic->isr_count = 1;
> +	} else {
> +		apic->irr_pending = !!count_vectors(apic->regs + APIC_IRR);

What about:
		apic->irr_pending = apic_search_irr(apic) != -1;
instead? (more in line with the logic in apic_clear_irr())


Related to this, I wonder if we need to ensure to execute
kvm_x86_ops->sync_pir_to_irr() just before apicv_active transitions
from true to false, so that we don't miss an interrupt and irr_pending
is set correctly in this function (on Intel at least).

Hmm... there seems to be other stuff as well, that depends on
vcpu->arch.apicv_active, which is not updated on a transition. For
example: posted interrupts, CR8 intercept, and a potential asymmetry
via avic_vcpu_load()/avic_vcpu_put() because the bottom half
of just one of the two functions may be skipped...

Do these need to be handled in some way?

Regards
Jan

> +		apic->isr_count = count_vectors(apic->regs + APIC_ISR);
> +	}
> +}
> +EXPORT_SYMBOL(kvm_apic_update_apicv);
> +
>  void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
>  {
>  	struct kvm_lapic *apic = vcpu->arch.apic;
> @@ -2170,8 +2186,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
>  		kvm_lapic_set_reg(apic, APIC_ISR + 0x10 * i, 0);
>  		kvm_lapic_set_reg(apic, APIC_TMR + 0x10 * i, 0);
>  	}
> -	apic->irr_pending = vcpu->arch.apicv_active;
> -	apic->isr_count = vcpu->arch.apicv_active ? 1 : 0;
> +	kvm_apic_update_apicv(vcpu);
>  	apic->highest_isr_cache = -1;
>  	update_divide_count(apic);
>  	atomic_set(&apic->lapic_timer.pending, 0);
> @@ -2433,9 +2448,7 @@ int kvm_apic_set_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s)
>  	apic_manage_nmi_watchdog(apic, kvm_lapic_get_reg(apic, APIC_LVT0));
>  	update_divide_count(apic);
>  	start_apic_timer(apic);
> -	apic->irr_pending = true;
> -	apic->isr_count = vcpu->arch.apicv_active ?
> -				1 : count_vectors(apic->regs + APIC_ISR);
> +	kvm_apic_update_apicv(vcpu);
>  	apic->highest_isr_cache = -1;
>  	if (vcpu->arch.apicv_active) {
>  		kvm_x86_ops->apicv_post_state_restore(vcpu);
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index ff6ef9c3d760..b657605cfec0 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -88,6 +88,7 @@ void kvm_apic_update_ppr(struct kvm_vcpu *vcpu);
>  int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq,
>  		     struct dest_map *dest_map);
>  int kvm_apic_local_deliver(struct kvm_lapic *apic, int lvt_type);
> +void kvm_apic_update_apicv(struct kvm_vcpu *vcpu);
>  
>  bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,
>  		struct kvm_lapic_irq *irq, int *r, struct dest_map *dest_map);
>