We going to allow L2 guest to use L1's kvm-clock clocksource, which is
a pvclock clocksource, as a stable one if it's stable in L1.
Therefore, we need to know when L1's kvm-clock becomes stable/unstable
to make it stable/unstable in L2 as well.
Do it, by adding tracking stability flag in pvclock
Signed-off-by: Denis Plotnikov <dplotnikov@xxxxxxxxxxxxx>
---
arch/x86/kernel/pvclock.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index ab54c92..c73e5a5 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -22,6 +22,7 @@
#include <linux/gfp.h>
#include <linux/bootmem.h>
#include <linux/nmi.h>
+#include <linux/cs_notifier.h>
#include <asm/fixmap.h>
#include <asm/pvclock.h>
@@ -73,6 +74,8 @@ u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
return flags & valid_flags;
}
+static atomic64_t clocksource_stable = ATOMIC64_INIT(0);
+
u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src,
u64 *cycles_stamp)
{
@@ -96,10 +99,20 @@ u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src,
pvclock_touch_watchdogs();
}
- if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
- (flags & PVCLOCK_TSC_STABLE_BIT))
- return ret;
+ if (likely(valid_flags & PVCLOCK_TSC_STABLE_BIT)) {
+ bool stable_now = !!(flags & PVCLOCK_TSC_STABLE_BIT);
+ bool stable_last = (bool) atomic64_read(&clocksource_stable);
+
+ if (unlikely(stable_now != stable_last)) {
+ /* send notification once */
+ if (stable_last == atomic64_cmpxchg(
+ &clocksource_stable, stable_last, stable_now))
+ clocksource_changes_notify();
+ }
+ if (stable_now)
+ return ret;
+ }
/*
* Assumption here is that last_value, a global accumulator, always goes
* forward. If we are less than that, we should not be much smaller.
--
2.7.4
