linux-kernel - Re: [PATCH v5 1/3] KVM: X86: Save&restore the triple fault request

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Date:   Wed, 6 Apr 2022 21:51:14 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Chenyi Qiang <chenyi.qiang@...el.com>
Cc:     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>,
        Xiaoyao Li <xiaoyao.li@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/3] KVM: X86: Save&restore the triple fault request

On Tue, Apr 05, 2022, Sean Christopherson wrote:
> On Fri, Mar 18, 2022, Chenyi Qiang wrote:
> > @@ -4903,7 +4906,8 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
> >  			      | KVM_VCPUEVENT_VALID_SIPI_VECTOR
> >  			      | KVM_VCPUEVENT_VALID_SHADOW
> >  			      | KVM_VCPUEVENT_VALID_SMM
> > -			      | KVM_VCPUEVENT_VALID_PAYLOAD))
> > +			      | KVM_VCPUEVENT_VALID_PAYLOAD
> > +			      | KVM_VCPUEVENT_TRIPLE_FAULT))
> >  		return -EINVAL;
> >  
> >  	if (events->flags & KVM_VCPUEVENT_VALID_PAYLOAD) {
> > @@ -4976,6 +4980,9 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
> >  		}
> >  	}
> >  
> > +	if (events->flags & KVM_VCPUEVENT_TRIPLE_FAULT)
> > +		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
> > +
> >  	kvm_make_request(KVM_REQ_EVENT, vcpu);
> 
> Looks correct, but this really needs a selftest, at least for the SET path since
> the intent is to use that for the NOTIFY handling.  Doesn't need to be super fancy,
> e.g. do port I/O from L2, inject a triple fault, and verify L1 sees the appropriate
> exit.

It finally dawned on me why all the other events use two "flags", i.e. an actual
flags entry of KVM_VCPUEVENT_VALID_* and then the value itself.  Userspace needs
to be able to _clear_ the request, not just set the request.  So this needs to
follow the existing pattern of adding a VALID flag and then yet another field to
specify whether or not a triple fault is pending.