linux-kernel - Re: [PATCH v4 00/10] make L2's kvm-clock stable, get rid of pvclock_gtod

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Message-ID: <CALAqxLWGf6BAdji=rqKPnyvFzzUQscA5rXU8SY4RcWXymyVL1Q@mail.gmail.com>
Date:   Tue, 22 Aug 2017 12:50:06 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Denis Plotnikov <dplotnikov@...tuozzo.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        lkml <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>, rkagan@...tuozzo.com,
        den@...tuozzo.com, Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH v4 00/10] make L2's kvm-clock stable, get rid of
 pvclock_gtod_copy in KVM

On Mon, Aug 21, 2017 at 1:40 AM, Denis Plotnikov
<dplotnikov@...tuozzo.com> wrote:
> ping!
>

I still don't feel my questions have been well answered. Its really
not clear to me why, in order to allow the level-2 guest to use a vdso
that the answer is to export more data through the entire stack rather
then to make the kvmclock to be usable from the vsyscall.

So far for a problem statement, all I've got is:
"However, when using nested virtualization you have

        L0: bare-metal hypervisor (uses TSC)
        L1: nested hypervisor (uses kvmclock, can use vsyscall)
        L2: nested guest

and L2 cannot use vsyscall because it is not using the TSC."

Which is a start but doesn't really make it clear why the proposed
solution is best/necessary.

thanks
-john