From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [PATCH] kvm: kvmclock: let KVM_GET_CLOCK return whether the
 master clock is in use
Date: Wed, 9 Nov 2016 18:17:19 -0200
Message-ID: <20161109201716.GB25974@amt.cnet>
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 <20161109201248.GA25974@amt.cnet>
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Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
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On Wed, Nov 09, 2016 at 06:12:50PM -0200, Marcelo Tosatti wrote:
> On Wed, Nov 09, 2016 at 05:48:15PM +0100, Paolo Bonzini wrote:
> > Userspace can read the exact value of kvmclock by reading the TSC
> > and fetching the timekeeping parameters out of guest memory.  This
> > however is brittle and not necessary anymore with KVM 4.11.  
> 
> Hi Paolo,
> 
> Can you point to commit or explanation why that is not the case anymore?
> Thanks

I don't see how thats possible given the:

 * TSC 
 * TSC (timer interrupt + TSC deltas) (AKA host TSC clocksource and
 * CLOCK_MONOTONIC).
 
Clocks currently drift from each other (therefore are not monotonic).

Have you confirmed CLOCK_MONOTONIC_RAW and TSC are monotonic?