linux-kernel - Re: [PATCH 2/2] KVM: x86: Fix split-irqchip vs interrupt injection window request

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Message-ID: <5b422691-ffc5-d73a-1bda-f1ee61116756@redhat.com>
Date:   Thu, 15 Apr 2021 08:07:06 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Lai Jiangshan <jiangshanlai+lkml@...il.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        Filippo Sironi <sironi@...zon.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        "v4.7+" <stable@...r.kernel.org>,
        Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [PATCH 2/2] KVM: x86: Fix split-irqchip vs interrupt injection
 window request

On 15/04/21 02:59, Lai Jiangshan wrote:
> The next call to inject_pending_event() will reach here AT FIRST with
> vcpu->arch.exception.injected==false and vcpu->arch.exception.pending==false
> 
>>           ... if (!vcpu->arch.exception.pending) {
>>                   if (vcpu->arch.nmi_injected) {
>>                           static_call(kvm_x86_set_nmi)(vcpu);
>>                           can_inject = false;
>>                   } else if (vcpu->arch.interrupt.injected) {
>>                           static_call(kvm_x86_set_irq)(vcpu);
>>                           can_inject = false;
>
> And comes here and vcpu->arch.interrupt.injected is true for there is
> an interrupt queued by KVM_INTERRUPT for pure user irqchip. It then does
> the injection of the interrupt without checking the EFLAGS.IF.

Ok, understood now.  Yeah, that could be a problem for userspace irqchip 
so we should switch it to use pending_external_vector instead.  Are you 
going to write the patch or should I?

Thanks!

Paolo

> My question is that what stops the next call to inject_pending_event()
> to reach here when KVM_INTERRUPT is called with exepction pending.