linux-kernel - Re: [PATCH 0/2] KVM: SVM: Implement check_nested

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Date:   Wed, 15 Apr 2020 14:45:16 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Cathy Avery <cavery@...hat.com>
Cc:     wei.huang2@....com, Jim Mattson <jmattson@...gle.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 0/2] KVM: SVM: Implement check_nested_events for NMI

On 15/04/20 11:49, Vitaly Kuznetsov wrote:
> Not directly related to this series but I just noticed that we have the
> following comment in inject_pending_event():
> 
> 	/* try to inject new event if pending */
> 	if (vcpu->arch.exception.pending) {
>                 ...
> 		if (vcpu->arch.exception.nr == DB_VECTOR) {
> 			/*
> 			 * This code assumes that nSVM doesn't use
> 			 * check_nested_events(). If it does, the
> 			 * DR6/DR7 changes should happen before L1
> 			 * gets a #VMEXIT for an intercepted #DB in
> 			 * L2.  (Under VMX, on the other hand, the
> 			 * DR6/DR7 changes should not happen in the
> 			 * event of a VM-exit to L1 for an intercepted
> 			 * #DB in L2.)
> 			 */
> 			kvm_deliver_exception_payload(vcpu);
> 			if (vcpu->arch.dr7 & DR7_GD) {
> 				vcpu->arch.dr7 &= ~DR7_GD;
> 				kvm_update_dr7(vcpu);
> 			}
> 		}
> 
> 		kvm_x86_ops.queue_exception(vcpu);
> 	}
> 
> As we already implement check_nested_events() on SVM, do we need to do
> anything here? CC: Jim who added the guardian (f10c729ff9652).

It's (still) okay because we don't use check_nested_events() for exceptions.

Regarding this series, I think we should implement the NMI injection
test for VMX and see if it requires the same change as patch 2.

Paolo