diff options
| -rw-r--r-- | Documentation/lguest/lguest.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c index 64110797044..bb5e3c28d9d 100644 --- a/Documentation/lguest/lguest.c +++ b/Documentation/lguest/lguest.c @@ -172,6 +172,7 @@ static struct termios orig_term; * threads and so we need to make sure that changes visible to the Guest happen * in precise order. */ #define wmb() __asm__ __volatile__("" : : : "memory") +#define mb() __asm__ __volatile__("" : : : "memory") /* Convert an iovec element to the given type. * @@ -593,9 +594,23 @@ static unsigned wait_for_vq_desc(struct virtqueue *vq, /* OK, tell Guest about progress up to now. */ trigger_irq(vq); + /* OK, now we need to know about added descriptors. */ + vq->vring.used->flags &= ~VRING_USED_F_NO_NOTIFY; + + /* They could have slipped one in as we were doing that: make + * sure it's written, then check again. */ + mb(); + if (last_avail != vq->vring.avail->idx) { + vq->vring.used->flags |= VRING_USED_F_NO_NOTIFY; + break; + } + /* Nothing new? Wait for eventfd to tell us they refilled. */ if (read(vq->eventfd, &event, sizeof(event)) != sizeof(event)) errx(1, "Event read failed?"); + + /* We don't need to be notified again. */ + vq->vring.used->flags |= VRING_USED_F_NO_NOTIFY; } /* Check it isn't doing very strange things with descriptor numbers. */ |