diff options
| -rw-r--r-- | drivers/lguest/hypercalls.c | 21 | ||||
| -rw-r--r-- | drivers/lguest/interrupts_and_traps.c | 7 | ||||
| -rw-r--r-- | drivers/lguest/lg.h | 1 | ||||
| -rw-r--r-- | drivers/lguest/lguest.c | 52 | ||||
| -rw-r--r-- | include/linux/lguest.h | 4 |
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. */ |
