x86, vmi: TSC going backwards check in vmi clocksource

Impact: fix time warps under vmware

Similar to the check for TSC going backwards in the TSC clocksource,
we also need this check for VMI clocksource.

Signed-off-by: Alok N Kataria <akataria@vmware.com>
Cc: Zachary Amsden <zach@vmware.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: stable@kernel.org

diff --git a/arch/x86/kernel/vmiclock_32.c b/arch/x86/kernel/vmiclock_32.c
index c4c1f9e094027089373189f7e57cb7ede8149be9..bde106cae0a98c600498378db8420a9daafdc60f 100644 (file)
--- a/arch/x86/kernel/vmiclock_32.c
+++ b/arch/x86/kernel/vmiclock_32.c
@@ -283,10 +283,13 @@ void __devinit vmi_time_ap_init(void)
 #endif
 
 /** vmi clocksource */
+static struct clocksource clocksource_vmi;
 
 static cycle_t read_real_cycles(void)
 {
-       return vmi_timer_ops.get_cycle_counter(VMI_CYCLES_REAL);
+       cycle_t ret = (cycle_t)vmi_timer_ops.get_cycle_counter(VMI_CYCLES_REAL);
+       return ret >= clocksource_vmi.cycle_last ?
+               ret : clocksource_vmi.cycle_last;
 }
 
 static struct clocksource clocksource_vmi = {