linux-kernel - Re: [PATCH] x86/pvclock-xen: zero last

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Date:	Fri, 26 Nov 2010 14:29:40 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	"Xen-devel@...ts.xensource.com" <Xen-devel@...ts.xensource.com>,
	kvm-devel <kvm@...r.kernel.org>,
	Glauber Costa <glommer@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Olivier Hanesse <olivier.hanesse@...il.com>,
	Avi Kivity <avi@...hat.com>,
	Eelco Dolstra <e.dolstra@...elft.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/pvclock-xen: zero last_value on resume

On 11/26/2010 02:40 AM, Ingo Molnar wrote:
> * Jeremy Fitzhardinge <jeremy@...p.org> wrote:
>
>> On 10/26/2010 09:59 AM, Jeremy Fitzhardinge wrote:
>>> If the guest domain has been suspend/resumed or migrated, then the
>>> system clock backing the pvclock clocksource may revert to a smaller
>>> value (ie, can be non-monotonic across the migration/save-restore).
>>> Make sure we zero last_value in that case so that the domain
>>> continues to see clock updates.
>> Ping?  Looks like this fell through the gaps.
> Does not apply cleanly here - mind resending the latest version?

It rebased cleanly to 2.6.37-rc3.  You can pull it from:

  git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git pvclock-resume

Jeremy Fitzhardinge (1):
      x86/pvclock: zero last_value on resume

 arch/x86/include/asm/pvclock.h |    1 +
 arch/x86/kernel/pvclock.c      |    5 +++++
 arch/x86/xen/time.c            |    2 ++
 3 files changed, 8 insertions(+), 0 deletions(-)

Thanks,
	J

Subject: [PATCH] x86/pvclock: zero last_value on resume

If the guest domain has been suspend/resumed or migrated, then the
system clock backing the pvclock clocksource may revert to a smaller
value (ie, can be non-monotonic across the migration/save-restore).
Make sure we zero last_value in that case so that the domain
continues to see clock updates.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 7f7e577..31d84ac 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -11,6 +11,7 @@ unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src);
 void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
 			    struct pvclock_vcpu_time_info *vcpu,
 			    struct timespec *ts);
+void pvclock_resume(void);
 
 /*
  * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 008b91e..42eb330 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -83,6 +83,11 @@ unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
 
 static atomic64_t last_value = ATOMIC64_INIT(0);
 
+void pvclock_resume(void)
+{
+	atomic64_set(&last_value, 0);
+}
+
 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
 {
 	struct pvclock_shadow_time shadow;
diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index b2bb5aa..5da5e53 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -426,6 +426,8 @@ void xen_timer_resume(void)
 {
 	int cpu;
 
+	pvclock_resume();
+
 	if (xen_clockevent != &xen_vcpuop_clockevent)
 		return;
 


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