linux-kernel - Re: [PATCH] KVM: x86: call irq notifiers with directed EOI

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Date:	Wed, 18 Mar 2015 15:37:26 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Paolo Bonzini <pbonzini@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>, chao.zhou@...el.com
Subject: Re: [PATCH] KVM: x86: call irq notifiers with directed EOI

Radim Krčmář <rkrcmar@...hat.com> writes:

> kvm_ioapic_update_eoi() wasn't called if directed EOI was enabled.
> We need to do that for irq notifiers.  (Like with edge interrupts.)

Wow! It's interesting that this path is only hit with Xen as guest.
I always thought of directed EOI as a "security feature" since broadcast
could lead to interrupt storms (or something like that) :)

Bandan

> Fix it by skipping EOI broadcast only.
>
> Bug: https://bugzilla.kernel.org/show_bug.cgi?id=82211
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  arch/x86/kvm/ioapic.c | 4 +++-
>  arch/x86/kvm/lapic.c  | 3 +--
>  2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
> index b1947e0f3e10..46d4449772bc 100644
> --- a/arch/x86/kvm/ioapic.c
> +++ b/arch/x86/kvm/ioapic.c
> @@ -422,6 +422,7 @@ static void __kvm_ioapic_update_eoi(struct kvm_vcpu *vcpu,
>  			struct kvm_ioapic *ioapic, int vector, int trigger_mode)
>  {
>  	int i;
> +	struct kvm_lapic *apic = vcpu->arch.apic;
>  
>  	for (i = 0; i < IOAPIC_NUM_PINS; i++) {
>  		union kvm_ioapic_redirect_entry *ent = &ioapic->redirtbl[i];
> @@ -443,7 +444,8 @@ static void __kvm_ioapic_update_eoi(struct kvm_vcpu *vcpu,
>  		kvm_notify_acked_irq(ioapic->kvm, KVM_IRQCHIP_IOAPIC, i);
>  		spin_lock(&ioapic->lock);
>  
> -		if (trigger_mode != IOAPIC_LEVEL_TRIG)
> +		if (trigger_mode != IOAPIC_LEVEL_TRIG ||
> +		    kvm_apic_get_reg(apic, APIC_SPIV) & APIC_SPIV_DIRECTED_EOI)
>  			continue;
>  
>  		ASSERT(ent->fields.trig_mode == IOAPIC_LEVEL_TRIG);
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index bd4e34de24c7..4ee827d7bf36 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -833,8 +833,7 @@ int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2)
>  
>  static void kvm_ioapic_send_eoi(struct kvm_lapic *apic, int vector)
>  {
> -	if (!(kvm_apic_get_reg(apic, APIC_SPIV) & APIC_SPIV_DIRECTED_EOI) &&
> -	    kvm_ioapic_handles_vector(apic->vcpu->kvm, vector)) {
> +	if (kvm_ioapic_handles_vector(apic->vcpu->kvm, vector)) {
>  		int trigger_mode;
>  		if (apic_test_vector(vector, apic->regs + APIC_TMR))
>  			trigger_mode = IOAPIC_LEVEL_TRIG;
--
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