linux-kernel - Re: [PATCH 3/4] KVM: x86: introduce get_kvmclock

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Date:   Mon, 19 Sep 2016 19:33:45 +0300
From:   Roman Kagan <rkagan@...tuozzo.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
CC:     <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        <rkrcmar@...hat.com>, <den@...nvz.org>, <peterhornyack@...gle.com>
Subject: Re: [PATCH 3/4] KVM: x86: introduce get_kvmclock_ns

On Mon, Sep 19, 2016 at 01:39:12PM +0200, Paolo Bonzini wrote:
> Introduce a function that reads the exact nanoseconds value that is
> provided to the guest in kvmclock.  This crystallizes the notion of
> kvmclock as a thin veneer over a stable TSC, that the guest will
> (hopefully) convert with NTP.  In other words, kvmclock is *not* a
> paravirtualized host-to-guest NTP.
> 
> Drop the get_kernel_ns() function, that was used both to get the base
> value of the master clock and to get the current value of kvmclock.
> The former use is replaced by ktime_get_boot_ns(), the latter is
> the purpose of get_kernel_ns().
> 
> This also allows KVM to provide a Hyper-V time reference counter that
> is synchronized with the time that is computed from the TSC page.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/entry/vdso/vclock_gettime.c |  2 +-
>  arch/x86/include/asm/pvclock.h       |  5 ++--
>  arch/x86/kernel/pvclock.c            |  2 +-
>  arch/x86/kvm/hyperv.c                |  2 +-
>  arch/x86/kvm/x86.c                   | 48 +++++++++++++++++++++++++++---------
>  arch/x86/kvm/x86.h                   |  6 +----
>  6 files changed, 43 insertions(+), 22 deletions(-)

Reviewed-by: Roman Kagan <rkagan@...tuozzo.com>