uml: deal with host time going backwards

Protection against the host's time going backwards (eg, ntp activity on
the host) by keeping track of the time at the last tick and if it's
greater than the current time, keep time stopped until the host catches
up.

Cc: Nix <nix@esperi.org.uk>
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
index bee98f466d660543cd16d14ce355b6c2fc09db0a..dec5678fc17f7b65ef5b1113d8f6246f910bab79 100644 (file)
--- a/arch/um/os-Linux/time.c
+++ b/arch/um/os-Linux/time.c
@@ -106,6 +106,10 @@ static void deliver_alarm(void)
        unsigned long long this_tick = os_nsecs();
        int one_tick = UM_NSEC_PER_SEC / UM_HZ;
 
+       /* Protection against the host's time going backwards */
+       if ((last_tick != 0) && (this_tick < last_tick))
+               this_tick = last_tick;
+
        if (last_tick == 0)
                last_tick = this_tick - one_tick;
 
@@ -148,6 +152,9 @@ static int after_sleep_interval(struct timespec *ts)
                start_usecs = usec;
 
        start_usecs -= skew / UM_NSEC_PER_USEC;
+       if (start_usecs < 0)
+               start_usecs = 0;
+
        tv = ((struct timeval) { .tv_sec  = start_usecs / UM_USEC_PER_SEC,
                                 .tv_usec = start_usecs % UM_USEC_PER_SEC });
        interval = ((struct itimerval) { { 0, usec }, tv });