[Xen-devel] [PATCH] x86/pvclock-xen: zero last_value on resume

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

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.

[ I don't know if kvm needs an analogous fix or not. ]

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
Cc: Stable Kernel <stable@xxxxxxxxxx>
Reported-by: Eelco Dolstra <e.dolstra@xxxxxxxxxx>
Reported-by: Olivier Hanesse <olivier.hanesse@xxxxxxxxx>
Bisected-by: CÃdric Schieli <cschieli@xxxxxxxxx>
Tested-by: CÃdric Schieli <cschieli@xxxxxxxxx>

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index cd02f32..6226870 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -11,5 +11,6 @@ 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);
 
 #endif /* _ASM_X86_PVCLOCK_H */
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 239427c..a4f07c1 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -120,6 +120,11 @@ 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;

Attachment: x86-pvclock-resume.patch
Description: Text document

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