Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method
Date	2017-02-13 20:30 +0100
Message-ID	<tautY-7VL-11@gated-at.bofh.it> (permalink)
References	(5 earlier) <t9k3E-4oZ-21@gated-at.bofh.it> <t9moN-5Rn-11@gated-at.bofh.it> <t9o7f-73R-7@gated-at.bofh.it> <tajId-M9-9@gated-at.bofh.it> <tauaE-7Oj-59@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Mon, 13 Feb 2017, Andy Lutomirski wrote:

> On Sun, Feb 12, 2017 at 11:49 PM, Dexuan Cui <decui@microsoft.com> wrote:
> >> From: Thomas Gleixner [mailto:tglx@linutronix.de]
> >> Sent: Saturday, February 11, 2017 02:02
> >>  ...
> >> That's important if the stuff happens cross CPU. If the update happens on
> >> the same CPU then this is a different story and as there are VMexits
> >> involved they might provide the required ordering already. But I can't tell
> >> as I have no idea how that host side thing is done.
> >>
> >>       tglx
> >
> > IMO Hyper-V TSC page clocksource here seems pretty similar to KVM's pvclock,
> > So I would guess "the structure is only updated just before reentering the guest
> > after some VM event" (https://rwmj.wordpress.com/2010/10/15/kvm-pvclock/),
> > that is, the update should happen on the same CPU, I guess.
> 
> If the patch is correct, there is one of these shared by all vCPUs, so
> this is not a sufficient explanation.

Right, because that's ony ONE TSC page for the whole guest and then the seq
stuff really lacks barriers.

Thanks,

	tglx

Thread

[PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-02-09 15:20 +0100
  Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read  method Thomas Gleixner <tglx@linutronix.de> - 2017-02-09 18:10 +0100
    RE: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method Stephen Hemminger <sthemmin@microsoft.com> - 2017-02-09 19:30 +0100
      Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read  method Thomas Gleixner <tglx@linutronix.de> - 2017-02-10 15:10 +0100
        RE: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method Stephen Hemminger <sthemmin@microsoft.com> - 2017-02-10 17:40 +0100
          RE: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read  method Thomas Gleixner <tglx@linutronix.de> - 2017-02-10 19:30 +0100
            RE: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method Dexuan Cui <decui@microsoft.com> - 2017-02-13 09:00 +0100
              RE: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read  method Thomas Gleixner <tglx@linutronix.de> - 2017-02-13 10:30 +0100
              Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method Andy Lutomirski <luto@amacapital.net> - 2017-02-13 20:10 +0100
                Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read  method Thomas Gleixner <tglx@linutronix.de> - 2017-02-13 20:30 +0100
      Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-02-10 15:50 +0100
    RE: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method KY Srinivasan <kys@microsoft.com> - 2017-02-09 21:50 +0100
      Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method Andy Lutomirski <luto@amacapital.net> - 2017-02-10 00:00 +0100
        Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method Stephen Hemminger <stephen@networkplumber.org> - 2017-02-10 00:20 +0100
        Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-02-10 13:20 +0100
    Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-02-10 12:10 +0100
      Re: [PATCH 2/2] x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read  method Thomas Gleixner <tglx@linutronix.de> - 2017-02-10 12:40 +0100

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