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-rw-r--r--drivers/lguest/hypercalls.c21
-rw-r--r--drivers/lguest/interrupts_and_traps.c7
-rw-r--r--drivers/lguest/lg.h1
-rw-r--r--drivers/lguest/lguest.c52
-rw-r--r--include/linux/lguest.h4
5 files changed, 60 insertions, 25 deletions
diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c
index 7a5299f..db6caac 100644
--- a/drivers/lguest/hypercalls.c
+++ b/drivers/lguest/hypercalls.c
@@ -64,14 +64,6 @@ static void do_hcall(struct lguest *lg, struct lguest_regs *regs)
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
@@ -235,6 +227,9 @@ static void initialize(struct lguest *lg)
|| 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)
@@ -293,3 +288,13 @@ void do_hypercalls(struct lguest *lg)
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");
+}
diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index bd0091b..49787e9 100644
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -175,6 +175,13 @@ void maybe_do_interrupt(struct lguest *lg)
* the stack as well: virtual interrupts never do. */
set_guest_interrupt(lg, idt->a, idt->b, 0);
}
+
+ /* Every time we deliver an interrupt, we update the timestamp in the
+ * Guest's lguest_data struct. It would be better for the Guest if we
+ * did this more often, but it can actually be quite slow: doing it
+ * here is a compromise which means at least it gets updated every
+ * timer interrupt. */
+ write_timestamp(lg);
}
/*H:220 Now we've got the routines to deliver interrupts, delivering traps
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 269116e..64f0abe 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -256,6 +256,7 @@ unsigned long get_dma_buffer(struct lguest *lg, unsigned long key,
/* hypercalls.c: */
void do_hypercalls(struct lguest *lg);
+void write_timestamp(struct lguest *lg);
/*L:035
* Let's step aside for the moment, to study one important routine that's used
diff --git a/drivers/lguest/lguest.c b/drivers/lguest/lguest.c
index 3386b0e..1bc1546 100644
--- a/drivers/lguest/lguest.c
+++ b/drivers/lguest/lguest.c
@@ -643,21 +643,42 @@ static void __init lguest_init_IRQ(void)
* 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. */
@@ -665,8 +686,11 @@ static struct clocksource lguest_clock = {
.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);
@@ -742,24 +766,21 @@ static void lguest_time_init(void)
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);
@@ -996,7 +1017,6 @@ __init void lguest_init(void *boot)
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(). */
diff --git a/include/linux/lguest.h b/include/linux/lguest.h
index e76c151..157ad64 100644
--- a/include/linux/lguest.h
+++ b/include/linux/lguest.h
@@ -17,7 +17,6 @@
#define LHCALL_TS 8
#define LHCALL_SET_CLOCKEVENT 9
#define LHCALL_HALT 10
-#define LHCALL_GET_WALLCLOCK 11
#define LHCALL_BIND_DMA 12
#define LHCALL_SEND_DMA 13
#define LHCALL_SET_PTE 14
@@ -88,6 +87,9 @@ struct lguest_data
* this address would normally be found. */
unsigned long cr2;
+ /* Wallclock time set by the Host. */
+ struct timespec time;
+
/* Async hypercall ring. Instead of directly making hypercalls, we can
* place them in here for processing the next time the Host wants.
* This batching can be quite efficient. */
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