linux-kernel - Re: [PATCH v2 3/3] KVM: X86: Let's harden the ipi fastpath condition edge-trigger mode

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Message-ID: <CANRm+CyecU4KYxNv77WGsiUB35r4TDNnLk7m_GLv=HvDCOGOLQ@mail.gmail.com>
Date:   Wed, 9 Jun 2021 10:08:19 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v2 3/3] KVM: X86: Let's harden the ipi fastpath condition
 edge-trigger mode

On Wed, 9 Jun 2021 at 00:35, Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Mon, Jun 07, 2021, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > Let's harden the ipi fastpath condition edge-trigger mode.
>
> Can you elaborate on the motivation for this patch?
>
> Intel's SDM states that the trigger mode is ignored for all IPIs except INIT,
> and even clarifies that the local xAPIC will override the bit and send the IPI
> as edge-triggered.
>
> AMD's APM on the other hand explicitly lists level-triggered Fixed IPIs as a
> valid ICR combination.
>
> Regardless of which of the two conflicting specs we want KVM to emulate (which
> is currently AMD), I don't see why the fastpath code should care, as I can't
> find anything in the kvm_apic_send_ipi() path that would go awry if it's called
> from the fastpath for a level-triggered IPI.

Fair enough.

    Wanpeng