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: <2a643f94-d159-c1ac-6bd2-cc6b45372630@redhat.com>
Date:   Tue, 8 Jun 2021 19:40:52 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        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 08/06/21 18:35, Sean Christopherson wrote:
> Related side topic, anyone happen to know if KVM (and Qemu's) emulation of IPIs
> intentionally follows AMD instead of Intel?  I suspect it's unintentional,
> especially since KVM's initial xAPIC emulation came from Intel.  Not that it's
> likely to matter, but allowing level-triggered IPIs is bizarre, e.g. getting an
> EOI sent to the right I/O APIC at the right time via a level-triggered IPI seems
> extremely convoluted.

QEMU traditionally followed AMD a bit more than Intel for historical 
reasons.  Probably the code went QEMU->Xen->KVM even though it was 
contributed by Intel.

Paolo