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

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Message-ID: <87zhbdw02i.fsf@vitty.brq.redhat.com>
Date:   Wed, 15 Apr 2020 11:49:25 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Cathy Avery <cavery@...hat.com>, pbonzini@...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

Cathy Avery <cavery@...hat.com> writes:

> Moved nested NMI exit to new check_nested_events.
> The second patch fixes the NMI pending race condition that now occurs.
>
> Cathy Avery (2):
>   KVM: SVM: Implement check_nested_events for NMI
>   KVM: x86: check_nested_events if there is an injectable NMI
>

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).

>  arch/x86/kvm/svm/nested.c | 21 +++++++++++++++++++++
>  arch/x86/kvm/svm/svm.c    |  2 +-
>  arch/x86/kvm/svm/svm.h    | 15 ---------------
>  arch/x86/kvm/x86.c        | 15 +++++++++++----
>  4 files changed, 33 insertions(+), 20 deletions(-)

-- 
Vitaly