linux-kernel - Re: [PATCH 2/2] kvm: nVMX: Introduce KVM_CAP

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Message-ID: <724a2ae2-e38f-148c-ce29-9869b2ab535f@redhat.com>
Date:   Sat, 28 Apr 2018 02:42:02 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     "Raslan, KarimAllah" <karahmed@...zon.de>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>
Subject: Re: [PATCH 2/2] kvm: nVMX: Introduce KVM_CAP_STATE

On 27/04/2018 17:19, Jim Mattson wrote:
> 
> If the default treatment of SMIs and SMM (see Section 34.14) is
> active, the VMX-preemption timer counts across an SMI to VMX non-root
> operation, subsequent execution in SMM, and the return from SMM via
> the RSM instruction. However, the timer can cause a VM exit only from
> VMX non-root operation. If the timer expires during SMI, in SMM, or
> during RSM, a timer-induced VM exit occurs immediately after RSM with
> its normal priority unless it is blocked based on activity state
> (Section 25.2).
> 
> So, there's no loophole here that allows us to reset the VMX
> preemption timer when restoring nested state.

Or when an SMI occurs.  So the expiration TSC of the preemption timer
should be stored into an "artificial" field of the vmcs12 at vmentry
time and later reused.

vmx->nested.smm.guest_node should also be saved...

Paolo

> As a follow-on change, we should probably fix this.