Re: [RFC PATCH V2 8/8] vhost: event suppression for packed ring
From: Jason Wang
Date: Thu Mar 29 2018 - 22:46:39 EST
On 2018å03æ30æ 10:05, Tiwei Bie wrote:
On Mon, Mar 26, 2018 at 11:38:53AM +0800, Jason Wang wrote:
This patch introduces basic support for event suppression aka driver
and device area. Compile tested only.
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
[...]
+
+static bool vhost_notify_packed(struct vhost_dev *dev,
+ struct vhost_virtqueue *vq)
+{
+ __virtio16 event_off_wrap, event_flags;
+ __u16 old, new;
+ bool v, wrap;
+ int off;
+
+ /* 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->desc_event_flags) < 0) {
+ vq_err(vq, "Failed to get driver desc_event_flags");
+ return true;
+ }
+
+ if (!(event_flags & cpu_to_vhost16(vq, RING_EVENT_FLAGS_DESC)))
+ return event_flags ==
+ cpu_to_vhost16(vq, RING_EVENT_FLAGS_ENABLE);
Maybe it would be better to not use '&' here. Because these flags
are not defined as bits which can be ORed or ANDed. Instead, they
are defined as values:
0x0 enable
0x1 disable
0x2 desc
0x3 reserved
Yes the code seems tricky. Let me fix it in next version.
+
+ /* Read desc event flags before event_off and event_wrap */
+ smp_rmb();
+
+ if (vhost_get_avail(vq, event_off_wrap,
+ &vq->driver_event->desc_event_off_warp) < 0) {
+ vq_err(vq, "Failed to get driver desc_event_off/wrap");
+ return true;
+ }
+
+ off = vhost16_to_cpu(vq, event_off_wrap);
+
+ wrap = off & 0x1;
+ off >>= 1;
Based on the below definitions in spec, wrap counter is
the most significant bit.
struct pvirtq_event_suppress {
le16 {
desc_event_off : 15; /* Descriptor Ring Change Event Offset */
desc_event_wrap : 1; /* Descriptor Ring Change Event Wrap Counter */
} desc; /* If desc_event_flags set to RING_EVENT_FLAGS_DESC */
le16 {
desc_event_flags : 2, /* Descriptor Ring Change Event Flags */
reserved : 14; /* Reserved, set to 0 */
} flags;
};
Will fix this in next version.
+
+
+ old = vq->signalled_used;
+ v = vq->signalled_used_valid;
+ new = vq->signalled_used = vq->last_used_idx;
+ vq->signalled_used_valid = true;
+
+ if (unlikely(!v))
+ return true;
+
+ return vhost_vring_packed_need_event(vq, new, old, off) &&
+ wrap == vq->used_wrap_counter;
+}
+
+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)
{
@@ -2789,7 +2911,17 @@ static bool vhost_enable_notify_packed(struct vhost_dev *dev,
__virtio16 flags;
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;
+
+ flags = cpu_to_vhost16(vq, RING_EVENT_FLAGS_ENABLE);
+ ret = vhost_update_device_flags(vq, flags);
+ if (ret) {
+ vq_err(vq, "Failed to enable notification at %p: %d\n",
+ &vq->device_event->desc_event_flags, ret);
+ return false;
+ }
/* They could have slipped one in as we were doing that: make
* sure it's written, then check again. */
@@ -2855,7 +2987,18 @@ 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->desc_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 8a9df4f..02d7a36 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;
Do you think it'd be better to name the desc type as
struct vring_packed_desc?
Ok. Will do.
And it will be consistent
with other names, like:
struct vring_packed;
struct vring_packed_desc_event;
};
- 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..7cdbf06 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 desc_event_off_warp;
+ /* Descriptor Ring Change Event Flags */
+ __virtio16 desc_event_flags;
Do you think it'd be better to remove the prefix (desc_event_) for
the fields. And it will be consistent with other definitions, e.g.:
struct vring_packed_desc {
/* Buffer Address. */
__virtio64 addr;
/* Buffer Length. */
__virtio32 len;
/* Buffer ID. */
__virtio16 id;
/* The flags depending on descriptor type. */
__virtio16 flags;
};
Yes. Let me do it in next version.
Thanks for the review!
+};
+
/* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
struct vring_desc {
/* Address (guest-physical). */
--
2.7.4