[PATCH 1/3] xen/arm: introduce xen_read_wallclock
Stefano Stabellini
sstabellini at kernel.org
Fri Nov 6 07:09:53 PST 2015
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 at eu.citrix.com>
>
> 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(¶virt_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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