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Message-ID: <013655c0-6950-8937-7489-95f9b0583642@redhat.com>
Date: Fri, 30 Mar 2018 10:46:24 +0800
From: Jason Wang <jasowang@...hat.com>
To: Tiwei Bie <tiwei.bie@...el.com>
Cc: mst@...hat.com, virtualization@...ts.linux-foundation.org,
kvm@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH V2 8/8] vhost: event suppression for packed ring
On 2018年03月30日 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@...hat.com>
>> ---
> [...]
>> +
>> +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
>>
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