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Subject: Re: [PATCH 2/2] KVM: x86: Fix split-irqchip vs interrupt injection
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To:     Lai Jiangshan <jiangshanlai+lkml@gmail.com>,
        Sean Christopherson <seanjc@google.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, kvm@vger.kernel.org,
        Filippo Sironi <sironi@amazon.de>,
        David Woodhouse <dwmw@amazon.co.uk>,
        "v4.7+" <stable@vger.kernel.org>,
        Wanpeng Li <wanpengli@tencent.com>
References: <20201127112114.3219360-1-pbonzini@redhat.com>
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 <CAJhGHyAcnwkCfTcnxXcgAHnF=wPbH2EDp7H+e74ce+oNOWJ=_Q@mail.gmail.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <80b013dc-0078-76f4-1299-3cff261ef7d8@redhat.com>
Date:   Tue, 13 Apr 2021 14:15:12 +0200
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On 13/04/21 13:03, Lai Jiangshan wrote:
> This patch claims that it has a place to
> stash the IRQ when EFLAGS.IF=0, but inject_pending_event() seams to ignore
> EFLAGS.IF and queues the IRQ to the guest directly in the first branch
> of using "kvm_x86_ops.set_irq(vcpu)".

This is only true for pure-userspace irqchip.  For split-irqchip, in 
which case the "place to stash" the interrupt is 
vcpu->arch.pending_external_vector.

For pure-userspace irqchip, KVM_INTERRUPT only cares about being able to 
stash the interrupt in vcpu->arch.interrupt.injected.  It is indeed 
wrong for userspace to call KVM_INTERRUPT if the vCPU is not ready for 
interrupt injection, but KVM_INTERRUPT does not return an error.

Ignoring the fact that this would be incorrect use of the API, are you 
saying that the incorrect injection was not possible before this patch?

Paolo