Re: [PATCH 3/3] x86/xen: sync the CMOS RTC as well as the Xen wallclock

[John Stultz]

On 05/14/2013 11:00 AM, David Vrabel wrote:
> On 14/05/13 18:24, John Stultz wrote:
> > On 05/13/2013 10:56 AM, David Vrabel wrote:
> > > From: David Vrabel <david.vrabel@xxxxxxxxxx>
> > >
> > > If NTP is used in dom0 and it is synchronized to its clock source,
> > > then the kernel will periodically synchronize the Xen wallclock with
> > > the system time.  Updates to the Xen wallclock do not persist across
> > > reboots, so also synchronize the CMOS RTC (as on bare metal).
> > >
> > > Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> > > ---
> > >    arch/x86/xen/time.c |   11 ++++++++++-
> > >    1 files changed, 10 insertions(+), 1 deletions(-)
> > >
> > > diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> > > index a1947ac..4656165 100644
> > > --- a/arch/x86/xen/time.c
> > > +++ b/arch/x86/xen/time.c
> > > @@ -14,6 +14,7 @@
> > >    #include <linux/kernel_stat.h>
> > >    #include <linux/math64.h>
> > >    #include <linux/gfp.h>
> > > +#include <linux/mc146818rtc.h>
> > >    
> > >    #include <asm/pvclock.h>
> > >    #include <asm/xen/hypervisor.h>
> > > @@ -199,17 +200,25 @@ static void xen_get_wallclock(struct timespec *now)
> > >    static int xen_set_wallclock(const struct timespec *now)
> > >    {
> > >    	struct xen_platform_op op;
> > > +	int ret;
> > >    
> > >    	/* do nothing for domU */
> > >    	if (!xen_initial_domain())
> > >    		return -1;
> > >    
> > > +	/* Set the Xen wallclock. */
> > >    	op.cmd = XENPF_settime;
> > >    	op.u.settime.secs = now->tv_sec;
> > >    	op.u.settime.nsecs = now->tv_nsec;
> > >    	op.u.settime.system_time = xen_clocksource_read();
> > >    
> > > -	return HYPERVISOR_dom0_op(&op);
> > > +	ret = HYPERVISOR_dom0_op(&op);
> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	/* Set the hardware RTC. */
> > > +	return mach_set_rtc_mmss(now);
> > Sorry, just noticed one more thing while applying this. Do all Xen
> > systems run on hardware that has the conventional CMOS clock?
> >
> > What happens if the bare-metal needs to use efi_set_rtc() or
> > vrtc_set_mmss() ?
> Ug. I hadn't considered that.  I'll have think some more on this.

Ok. I'll look forward to a future revision then and not queue this one.


Just FYI, here's what I rewrote the commit message to:

    x86/xen: Sync the CMOS RTC as well as the Xen wallclock

    Adjustments to Xen's persistent_clock via update_persistent_clock()
    don't actually persist, as the xen_set_walltime() just notifies
    other domN guests that it has been updated, and does not modify
    the underlying CMOS clock.

    Thus, this patch modifies xen_set_wallclock() so it will set
    the underlying CMOS clock when called from dom0, ensuring the
    persistent_clock will be correct on the next hardware boot.


I feel its a bit more clear, but feel free to tweak it as you see fit.

thanks
-john

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