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

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Message-ID: <f8875546-da53-fc36-d3da-5b5ff089ccc0@redhat.com>
Date:   Fri, 27 Apr 2018 12:03:21 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>,
        "Raslan, KarimAllah" <karahmed@...zon.de>
Cc:     "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 00:28, Jim Mattson wrote:
> The other thing that comes to mind is that there are some new fields
> in the VMCS12 since I first implemented this. One potentially
> troublesome field is the VMX preemption timer. If the current timer
> value is not saved on VM-exit, then it won't be stashed in the shadow
> VMCS12 by sync_vmcs12. Post-migration, the timer will be reset to its
> original value.
> 
> Do we care? Is this any different from what happens on real hardware
> when there's an SMI? According to the SDM, this appears to be exacty
> what happens when the dual-monitor treatment of SMIs and SMM is
> active, but it's not clear what happens with the default treatment of
> SMIs and SMM.

I think it should be the same, because the preemption timer countdown is
not part of the VMX-critical state.

Paolo