linux-kernel - Re: [RFC PATCH v3 01/11] KVM: Capture VM start

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Message-ID: <CAJHc60xZ9emY9Rs9ZbV+AH-Mjmkyg4JZU7V16TF48C-HJn+n4A@mail.gmail.com>
Date:   Mon, 10 Jan 2022 15:07:13 -0800
From:   Raghavendra Rao Ananta <rananta@...gle.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Reiji Watanabe <reijiw@...gle.com>, Marc Zyngier <maz@...nel.org>,
        Andrew Jones <drjones@...hat.com>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Peter Shier <pshier@...gle.com>,
        Ricardo Koller <ricarkol@...gle.com>,
        Oliver Upton <oupton@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [RFC PATCH v3 01/11] KVM: Capture VM start

On Fri, Jan 7, 2022 at 4:05 PM Jim Mattson <jmattson@...gle.com> wrote:
>
> On Fri, Jan 7, 2022 at 3:43 PM Raghavendra Rao Ananta
> <rananta@...gle.com> wrote:
> >
> > Hi Reiji,
> >
> > On Thu, Jan 6, 2022 at 10:07 PM Reiji Watanabe <reijiw@...gle.com> wrote:
> > >
> > > Hi Raghu,
> > >
> > > On Tue, Jan 4, 2022 at 11:49 AM Raghavendra Rao Ananta
> > > <rananta@...gle.com> wrote:
> > > >
> > > > Capture the start of the KVM VM, which is basically the
> > > > start of any vCPU run. This state of the VM is helpful
> > > > in the upcoming patches to prevent user-space from
> > > > configuring certain VM features after the VM has started
> > > > running.
>
> What about live migration, where the VM has already technically been
> started before the first call to KVM_RUN?

My understanding is that a new 'struct kvm' is created on the target
machine and this flag should be reset, which would allow the VMM to
restore the firmware registers. However, we would be running KVM_RUN
for the first time on the target machine, thus setting the flag.
So, you are right; It's more of a resume operation from the guest's
point of view. I guess the name of the variable is what's confusing
here.

Thanks,
Raghavendra