linux-kernel - Re: [PATCH 6/6] KVM: lapic: do not scan IRR when delivering an interrupt

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Message-ID: <bf9ce304-25e0-8fb4-78f9-6293b1d680e4@redhat.com>
Date:   Tue, 20 Dec 2016 18:11:13 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     rkrcmar@...hat.com, rkagan@...tuozzo.com, dplotnikov@...tuozzo.com
Subject: Re: [PATCH 6/6] KVM: lapic: do not scan IRR when delivering an
 interrupt

On 19/12/2016 10:47, Paolo Bonzini wrote:
> +	if (!test_bit(vector, vcpu_to_synic(vcpu)->auto_eoi_bitmap))
> +		apic_set_isr(vector, apic);
>  
> +	apic_clear_irr(vector, apic);
> +	__apic_update_ppr(apic, &ppr);

Hmm, EOI does apic_update_ppr, so for auto-EOI interrupts I think it's
safer to do apic_update_ppr instead.  You could have to interrupts
injected at the same time, and the lower-priority interrupt would be
lost if the higher-priority interrupt does automatic EOI.

Paolo