Re: [Xen-devel] [PATCH 1/3] xen/arm: introduce xen_read_wallclock

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 5 Nov 2015, Arnd Bergmann wrote:
> On Thursday 05 November 2015 17:09:43 Stefano Stabellini wrote:
> > Read the wallclock from the shared info page at boot time.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> 
> Please use the appropriate timespec64 based functions here,
> we are in the process of converting all callers of struct timespec.

OK, I can do that


> > ---
> > +static void xen_read_wallclock(struct timespec *ts)
> > +{
> > +   u32 version;
> > +   u64 delta;
> > +   struct timespec now;
> > +   struct shared_info *s = HYPERVISOR_shared_info;
> > +   struct pvclock_wall_clock *wall_clock = &(s->wc);
> 
> pvclock_wall_clock has a 'u32 sec', so that suffers from
> a potential overflow. We should try to avoid introducing that
> on ARM, and instead have a 64-bit seconds based version,
> or alternatively a 64-bit nanoseconds version (with no
> extra seconds) that is also sufficient.

Unfortunately this a preexisting ABI which is common with other existing
architectures (see arch/x86/kernel/pvclock.c:pvclock_read_wallclock). I
cannot just change it.


> >     struct vcpu_register_vcpu_info info;
> > @@ -218,6 +246,7 @@ static int __init xen_guest_init(void)
> >     struct shared_info *shared_info_page = NULL;
> >     struct resource res;
> >     phys_addr_t grant_frames;
> > +   struct timespec ts;
> >  
> >     if (!xen_domain())
> >             return 0;
> > @@ -291,6 +320,8 @@ static int __init xen_guest_init(void)
> >  
> >     pv_time_ops.steal_clock = xen_stolen_accounting;
> >     static_key_slow_inc(&paravirt_steal_enabled);
> > +   xen_read_wallclock(&ts);
> > +   do_settimeofday(&ts);
> >  
> 
> Once you can get a 64-bit time, call do_settimeofday64()
> here.

OK

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