else
guest_pagetable_flush_user(lg);
break;
- case LHCALL_GET_WALLCLOCK: {
- /* The Guest wants to know the real time in seconds since 1970,
- * in good Unix tradition. */
- struct timespec ts;
- ktime_get_real_ts(&ts);
- regs->eax = ts.tv_sec;
- break;
- }
case LHCALL_BIND_DMA:
/* BIND_DMA really wants four arguments, but it's the only call
* which does. So the Guest packs the number of buffers and
|| put_user(lg->guestid, &lg->lguest_data->guestid))
kill_guest(lg, "bad guest page %p", lg->lguest_data);
+ /* We write the current time into the Guest's data page once now. */
+ write_timestamp(lg);
+
/* This is the one case where the above accesses might have been the
* first write to a Guest page. This may have caused a copy-on-write
* fault, but the Guest might be referring to the old (read-only)
clear_hcall(lg);
}
}
+
+/* This routine supplies the Guest with time: it's used for wallclock time at
+ * initial boot and as a rough time source if the TSC isn't available. */
+void write_timestamp(struct lguest *lg)
+{
+ struct timespec now;
+ ktime_get_real_ts(&now);
+ if (put_user(now, &lg->lguest_data->time))
+ kill_guest(lg, "Writing timestamp");
+}
* Time.
*
* It would be far better for everyone if the Guest had its own clock, but
- * until then it must ask the Host for the time.
+ * until then the Host gives us the time on every interrupt.
*/
static unsigned long lguest_get_wallclock(void)
{
- return hcall(LHCALL_GET_WALLCLOCK, 0, 0, 0);
+ return lguest_data.time.tv_sec;
}
-/* If the Host tells us we can trust the TSC, we use that, otherwise we simply
- * use the imprecise but reliable "jiffies" counter. */
static cycle_t lguest_clock_read(void)
{
+ unsigned long sec, nsec;
+
+ /* If the Host tells the TSC speed, we can trust that. */
if (lguest_data.tsc_khz)
return native_read_tsc();
- else
- return jiffies;
+
+ /* If we can't use the TSC, we read the time value written by the Host.
+ * Since it's in two parts (seconds and nanoseconds), we risk reading
+ * it just as it's changing from 99 & 0.999999999 to 100 and 0, and
+ * getting 99 and 0. As Linux tends to come apart under the stress of
+ * time travel, we must be careful: */
+ do {
+ /* First we read the seconds part. */
+ sec = lguest_data.time.tv_sec;
+ /* This read memory barrier tells the compiler and the CPU that
+ * this can't be reordered: we have to complete the above
+ * before going on. */
+ rmb();
+ /* Now we read the nanoseconds part. */
+ nsec = lguest_data.time.tv_nsec;
+ /* Make sure we've done that. */
+ rmb();
+ /* Now if the seconds part has changed, try again. */
+ } while (unlikely(lguest_data.time.tv_sec != sec));
+
+ /* Our non-TSC clock is in real nanoseconds. */
+ return sec*1000000000ULL + nsec;
}
/* This is what we tell the kernel is our clocksource. */
.name = "lguest",
.rating = 400,
.read = lguest_clock_read,
+ .mask = CLOCKSOURCE_MASK(64),
+ .mult = 1,
};
+/* The "scheduler clock" is just our real clock, adjusted to start at zero */
static unsigned long long lguest_sched_clock(void)
{
return cyc2ns(&lguest_clock, lguest_clock_read() - clock_base);
set_irq_handler(0, lguest_time_irq);
/* Our clock structure look like arch/i386/kernel/tsc.c if we can use
- * the TSC, otherwise it looks like kernel/time/jiffies.c. Either way,
- * the "rating" is initialized so high that it's always chosen over any
- * other clocksource. */
+ * the TSC, otherwise it's a dumb nanosecond-resolution clock. Either
+ * way, the "rating" is initialized so high that it's always chosen
+ * over any other clocksource. */
if (lguest_data.tsc_khz) {
lguest_clock.shift = 22;
lguest_clock.mult = clocksource_khz2mult(lguest_data.tsc_khz,
lguest_clock.shift);
- lguest_clock.mask = CLOCKSOURCE_MASK(64);
lguest_clock.flags = CLOCK_SOURCE_IS_CONTINUOUS;
- } else {
- /* To understand this, start at kernel/time/jiffies.c... */
- lguest_clock.shift = 8;
- lguest_clock.mult = (((u64)NSEC_PER_SEC<<8)/ACTHZ) << 8;
- lguest_clock.mask = CLOCKSOURCE_MASK(32);
}
clock_base = lguest_clock_read();
clocksource_register(&lguest_clock);
+ /* Now we've set up our clock, we can use it as the scheduler clock */
+ paravirt_ops.sched_clock = lguest_sched_clock;
+
/* We can't set cpumask in the initializer: damn C limitations! Set it
* here and register our timer device. */
lguest_clockevent.cpumask = cpumask_of_cpu(0);
paravirt_ops.time_init = lguest_time_init;
paravirt_ops.set_lazy_mode = lguest_lazy_mode;
paravirt_ops.wbinvd = lguest_wbinvd;
- paravirt_ops.sched_clock = lguest_sched_clock;
/* Now is a good time to look at the implementations of these functions
* before returning to the rest of lguest_init(). */
projects / linux-2.6 / commitdiff