[RFC V5 PATCH 8/8] vhost: event suppression for packed ring

Jason Wang
2018-05-29T02:10:30Z

This patch introduces basic support for event suppression aka driver
and device area.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/vhost/vhost.c | 191 ++++++++++++++++++++++++++++++++++++---
drivers/vhost/vhost.h | 10 +-
include/uapi/linux/virtio_ring.h | 19 ++++
3 files changed, 204 insertions(+), 16 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index a36e5ad2..112f680 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1112,10 +1112,15 @@ static int vq_access_ok_packed(struct vhost_virtqueue *vq, unsigned int num,
struct vring_used __user *used)
{
struct vring_desc_packed *packed = (struct vring_desc_packed *)desc;
+ struct vring_packed_desc_event *driver_event =
+ (struct vring_packed_desc_event *)avail;
+ struct vring_packed_desc_event *device_event =
+ (struct vring_packed_desc_event *)used;

- /* FIXME: check device area and driver area */
return access_ok(VERIFY_READ, packed, num * sizeof(*packed)) &&
- access_ok(VERIFY_WRITE, packed, num * sizeof(*packed));
+ access_ok(VERIFY_WRITE, packed, num * sizeof(*packed)) &&
+ access_ok(VERIFY_READ, driver_event, sizeof(*driver_event)) &&
+ access_ok(VERIFY_WRITE, device_event, sizeof(*device_event));
}

static int vq_access_ok_split(struct vhost_virtqueue *vq, unsigned int num,
@@ -1190,14 +1195,27 @@ static bool iotlb_access_ok(struct vhost_virtqueue *vq,
return true;
}

-int vq_iotlb_prefetch(struct vhost_virtqueue *vq)
+int vq_iotlb_prefetch_packed(struct vhost_virtqueue *vq)
+{
+ int num = vq->num;
+
+ return iotlb_access_ok(vq, VHOST_ACCESS_RO, (u64)(uintptr_t)vq->desc,
+ num * sizeof(*vq->desc), VHOST_ADDR_DESC) &&
+ iotlb_access_ok(vq, VHOST_ACCESS_WO, (u64)(uintptr_t)vq->desc,
+ num * sizeof(*vq->desc), VHOST_ADDR_DESC) &&
+ iotlb_access_ok(vq, VHOST_ACCESS_RO,
+ (u64)(uintptr_t)vq->driver_event,
+ sizeof(*vq->driver_event), VHOST_ADDR_AVAIL) &&
+ iotlb_access_ok(vq, VHOST_ACCESS_WO,
+ (u64)(uintptr_t)vq->device_event,
+ sizeof(*vq->device_event), VHOST_ADDR_USED);
+}
+
+int vq_iotlb_prefetch_split(struct vhost_virtqueue *vq)
{
size_t s = vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
unsigned int num = vq->num;

- if (!vq->iotlb)
- return 1;
-
return iotlb_access_ok(vq, VHOST_ACCESS_RO, (u64)(uintptr_t)vq->desc,
num * sizeof(*vq->desc), VHOST_ADDR_DESC) &&
iotlb_access_ok(vq, VHOST_ACCESS_RO, (u64)(uintptr_t)vq->avail,
@@ -1209,6 +1227,17 @@ int vq_iotlb_prefetch(struct vhost_virtqueue *vq)
num * sizeof(*vq->used->ring) + s,
VHOST_ADDR_USED);
}
+
+int vq_iotlb_prefetch(struct vhost_virtqueue *vq)
+{
+ if (!vq->iotlb)
+ return 1;
+
+ if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
+ return vq_iotlb_prefetch_packed(vq);
+ else
+ return vq_iotlb_prefetch_split(vq);
+}
EXPORT_SYMBOL_GPL(vq_iotlb_prefetch);

/* Can we log writes? */
@@ -1730,6 +1759,50 @@ static int vhost_update_used_flags(struct vhost_virtqueue *vq)
return 0;
}

+static int vhost_update_device_flags(struct vhost_virtqueue *vq,
+ __virtio16 device_flags)
+{
+ void __user *flags;
+
+ if (vhost_put_user(vq, device_flags, &vq->device_event->flags,
+ VHOST_ADDR_USED) < 0)
+ return -EFAULT;
+ if (unlikely(vq->log_used)) {
+ /* Make sure the flag is seen before log. */
+ smp_wmb();
+ /* Log used flag write. */
+ flags = &vq->device_event->flags;
+ log_write(vq->log_base, vq->log_addr +
+ (flags - (void __user *)vq->device_event),
+ sizeof(vq->device_event->flags));
+ if (vq->log_ctx)
+ eventfd_signal(vq->log_ctx, 1);
+ }
+ return 0;
+}
+
+static int vhost_update_device_off_wrap(struct vhost_virtqueue *vq,
+ __virtio16 device_off_wrap)
+{
+ void __user *off_wrap;
+
+ if (vhost_put_user(vq, device_off_wrap, &vq->device_event->off_wrap,
+ VHOST_ADDR_USED) < 0)
+ return -EFAULT;
+ if (unlikely(vq->log_used)) {
+ /* Make sure the flag is seen before log. */
+ smp_wmb();
+ /* Log used flag write. */
+ off_wrap = &vq->device_event->off_wrap;
+ log_write(vq->log_base, vq->log_addr +
+ (off_wrap - (void __user *)vq->device_event),
+ sizeof(vq->device_event->off_wrap));
+ if (vq->log_ctx)
+ eventfd_signal(vq->log_ctx, 1);
+ }
+ return 0;
+}
+
static int vhost_update_avail_event(struct vhost_virtqueue *vq, u16 avail_event)
{
if (vhost_put_user(vq, cpu_to_vhost16(vq, vq->avail_idx),
@@ -2683,16 +2756,13 @@ int vhost_add_used_n(struct vhost_virtqueue *vq,
}
EXPORT_SYMBOL_GPL(vhost_add_used_n);

-static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
+static bool vhost_notify_split(struct vhost_dev *dev,
+ struct vhost_virtqueue *vq)
{
__u16 old, new;
__virtio16 event;
bool v;

- /* FIXME: check driver area */
- if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
- return true;
-
/* Flush out used index updates. This is paired
* with the barrier that the Guest executes when enabling
* interrupts. */
@@ -2725,6 +2795,64 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
return vring_need_event(vhost16_to_cpu(vq, event), new, old);
}

+static bool vhost_notify_packed(struct vhost_dev *dev,
+ struct vhost_virtqueue *vq)
+{
+ __virtio16 event_off_wrap, event_flags;
+ __u16 old, new, off_wrap;
+ bool v;
+
+ /* Flush out used descriptors updates. This is paired
+ * with the barrier that the Guest executes when enabling
+ * interrupts.
+ */
+ smp_mb();
+
+ if (vhost_get_avail(vq, event_flags,
+ &vq->driver_event->flags) < 0) {
+ vq_err(vq, "Failed to get driver desc_event_flags");
+ return true;
+ }
+
+ if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX))
+ return event_flags !=
+ cpu_to_vhost16(vq, RING_EVENT_FLAGS_DISABLE);
+
+ old = vq->signalled_used;
+ v = vq->signalled_used_valid;
+ new = vq->signalled_used = vq->last_used_idx;
+ vq->signalled_used_valid = true;
+
+ if (event_flags != cpu_to_vhost16(vq, RING_EVENT_FLAGS_DESC))
+ return event_flags !=
+ cpu_to_vhost16(vq, RING_EVENT_FLAGS_DISABLE);
+
+ /* Read desc event flags before event_off and event_wrap */
+ smp_rmb();
+
+ if (vhost_get_avail(vq, event_off_wrap,
+ &vq->driver_event->off_wrap) < 0) {
+ vq_err(vq, "Failed to get driver desc_event_off/wrap");
+ return true;
+ }
+
+ off_wrap = vhost16_to_cpu(vq, event_off_wrap);
+
+ if (unlikely(!v))
+ return true;
+
+ return vhost_vring_packed_need_event(vq, vq->used_wrap_counter,
+ off_wrap, new, old);
+}
+
+static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
+{
+ if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
+ return vhost_notify_packed(dev, vq);
+ else
+ return vhost_notify_split(dev, vq);
+}
+
/* This actually signals the guest, using eventfd. */
void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
@@ -2802,10 +2930,34 @@ static bool vhost_enable_notify_packed(struct vhost_dev *dev,
struct vhost_virtqueue *vq)
{
struct vring_desc_packed *d = vq->desc_packed + vq->avail_idx;
- __virtio16 flags;
+ __virtio16 flags = RING_EVENT_FLAGS_ENABLE;
int ret;

- /* FIXME: disable notification through device area */
+ if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
+ return false;
+ vq->used_flags &= ~VRING_USED_F_NO_NOTIFY;
+
+ if (vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) {
+ __virtio16 off_wrap = cpu_to_vhost16(vq, vq->avail_idx |
+ vq->avail_wrap_counter << 15);
+
+ ret = vhost_update_device_off_wrap(vq, off_wrap);
+ if (ret) {
+ vq_err(vq, "Failed to write to off warp at %p: %d\n",
+ &vq->device_event->off_wrap, ret);
+ return false;
+ }
+ /* Make sure off_wrap is wrote before flags */
+ smp_wmb();
+ flags = RING_EVENT_FLAGS_DESC;
+ }
+
+ ret = vhost_update_device_flags(vq, flags);
+ if (ret) {
+ vq_err(vq, "Failed to enable notification at %p: %d\n",
+ &vq->device_event->flags, ret);
+ return false;
+ }

/* They could have slipped one in as we were doing that: make
* sure it's written, then check again. */
@@ -2871,7 +3023,18 @@ EXPORT_SYMBOL_GPL(vhost_enable_notify);
static void vhost_disable_notify_packed(struct vhost_dev *dev,
struct vhost_virtqueue *vq)
{
- /* FIXME: disable notification through device area */
+ __virtio16 flags;
+ int r;
+
+ if (vq->used_flags & VRING_USED_F_NO_NOTIFY)
+ return;
+ vq->used_flags |= VRING_USED_F_NO_NOTIFY;
+
+ flags = cpu_to_vhost16(vq, RING_EVENT_FLAGS_DISABLE);
+ r = vhost_update_device_flags(vq, flags);
+ if (r)
+ vq_err(vq, "Failed to enable notification at %p: %d\n",
+ &vq->device_event->flags, r);
}

static void vhost_disable_notify_split(struct vhost_dev *dev,
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 7543a46..b920582 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -96,8 +96,14 @@ struct vhost_virtqueue {
struct vring_desc __user *desc;
struct vring_desc_packed __user *desc_packed;
};
- struct vring_avail __user *avail;
- struct vring_used __user *used;
+ union {
+ struct vring_avail __user *avail;
+ struct vring_packed_desc_event __user *driver_event;
+ };
+ union {
+ struct vring_used __user *used;
+ struct vring_packed_desc_event __user *device_event;
+ };
const struct vhost_umem_node *meta_iotlb[VHOST_NUM_ADDRS];
struct file *kick;
struct eventfd_ctx *call_ctx;
diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
index e297580..71c7a46 100644
--- a/include/uapi/linux/virtio_ring.h
+++ b/include/uapi/linux/virtio_ring.h
@@ -75,6 +75,25 @@ struct vring_desc_packed {
__virtio16 flags;
};

+/* Enable events */
+#define RING_EVENT_FLAGS_ENABLE 0x0
+/* Disable events */
+#define RING_EVENT_FLAGS_DISABLE 0x1
+/*
+ * Enable events for a specific descriptor
+ * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
+ * Only valid if VIRTIO_F_RING_EVENT_IDX has been negotiated.
+ */
+#define RING_EVENT_FLAGS_DESC 0x2
+/* The value 0x3 is reserved */
+
+struct vring_packed_desc_event {
+ /* Descriptor Ring Change Event Offset and Wrap Counter */
+ __virtio16 off_wrap;
+ /* Descriptor Ring Change Event Flags */
+ __virtio16 flags;
+};
+
/* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
struct vring_desc {
/* Address (guest-physical). */
--
2.7.4