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

On 05/15/2013 01:19 AM, Jan Beulich wrote:
On 14.05.13 at 19:24, John Stultz <john.stultz@xxxxxxxxxx> 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() ?
There's no EFI support in the upstream kernel yet when running
on Xen (the code that's in the kernel can't be used, as Dom0
can't directly invoke EFI runtime service functions).

And I don't think Xen is in any way prepared to run on
Moorestown, which afaict is where vrtc_set_mmss() comes into
the picture.


David: Would you resubmit this patch, adding this additional context in a comment?


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