Messages in this thread | | | Date | Tue, 27 Dec 2022 17:09:12 +0800 | Subject | Re: [PATCH 3/4] virtio_ring: introduce a per virtqueue waitqueue | From | Jason Wang <> |
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在 2022/12/27 15:19, Michael S. Tsirkin 写道: > On Tue, Dec 27, 2022 at 11:47:34AM +0800, Jason Wang wrote: >> On Tue, Dec 27, 2022 at 7:34 AM Michael S. Tsirkin <mst@redhat.com> wrote: >>> On Mon, Dec 26, 2022 at 03:49:07PM +0800, Jason Wang wrote: >>>> This patch introduces a per virtqueue waitqueue to allow driver to >>>> sleep and wait for more used. Two new helpers are introduced to allow >>>> driver to sleep and wake up. >>>> >>>> Signed-off-by: Jason Wang <jasowang@redhat.com> >>>> --- >>>> Changes since V1: >>>> - check virtqueue_is_broken() as well >>>> - use more_used() instead of virtqueue_get_buf() to allow caller to >>>> get buffers afterwards >>>> --- >>>> drivers/virtio/virtio_ring.c | 29 +++++++++++++++++++++++++++++ >>>> include/linux/virtio.h | 3 +++ >>>> 2 files changed, 32 insertions(+) >>>> >>>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c >>>> index 5cfb2fa8abee..9c83eb945493 100644 >>>> --- a/drivers/virtio/virtio_ring.c >>>> +++ b/drivers/virtio/virtio_ring.c >>>> @@ -13,6 +13,7 @@ >>>> #include <linux/dma-mapping.h> >>>> #include <linux/kmsan.h> >>>> #include <linux/spinlock.h> >>>> +#include <linux/wait.h> >>>> #include <xen/xen.h> >>>> >>>> #ifdef DEBUG >>>> @@ -60,6 +61,7 @@ >>>> "%s:"fmt, (_vq)->vq.name, ##args); \ >>>> /* Pairs with READ_ONCE() in virtqueue_is_broken(). */ \ >>>> WRITE_ONCE((_vq)->broken, true); \ >>>> + wake_up_interruptible(&(_vq)->wq); \ >>>> } while (0) >>>> #define START_USE(vq) >>>> #define END_USE(vq) >>>> @@ -203,6 +205,9 @@ struct vring_virtqueue { >>>> /* DMA, allocation, and size information */ >>>> bool we_own_ring; >>>> >>>> + /* Wait for buffer to be used */ >>>> + wait_queue_head_t wq; >>>> + >>>> #ifdef DEBUG >>>> /* They're supposed to lock for us. */ >>>> unsigned int in_use; >>>> @@ -2024,6 +2029,8 @@ static struct virtqueue *vring_create_virtqueue_packed( >>>> if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM)) >>>> vq->weak_barriers = false; >>>> >>>> + init_waitqueue_head(&vq->wq); >>>> + >>>> err = vring_alloc_state_extra_packed(&vring_packed); >>>> if (err) >>>> goto err_state_extra; >>>> @@ -2517,6 +2524,8 @@ static struct virtqueue *__vring_new_virtqueue(unsigned int index, >>>> if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM)) >>>> vq->weak_barriers = false; >>>> >>>> + init_waitqueue_head(&vq->wq); >>>> + >>>> err = vring_alloc_state_extra_split(vring_split); >>>> if (err) { >>>> kfree(vq); >>>> @@ -2654,6 +2663,8 @@ static void vring_free(struct virtqueue *_vq) >>>> { >>>> struct vring_virtqueue *vq = to_vvq(_vq); >>>> >>>> + wake_up_interruptible(&vq->wq); >>>> + >>>> if (vq->we_own_ring) { >>>> if (vq->packed_ring) { >>>> vring_free_queue(vq->vq.vdev, >>>> @@ -2863,4 +2874,22 @@ const struct vring *virtqueue_get_vring(struct virtqueue *vq) >>>> } >>>> EXPORT_SYMBOL_GPL(virtqueue_get_vring); >>>> >>>> +int virtqueue_wait_for_used(struct virtqueue *_vq) >>>> +{ >>>> + struct vring_virtqueue *vq = to_vvq(_vq); >>>> + >>>> + /* TODO: Tweak the timeout. */ >>>> + return wait_event_interruptible_timeout(vq->wq, >>>> + virtqueue_is_broken(_vq) || more_used(vq), HZ); >>> There's no good timeout. Let's not even go there, if device goes >>> bad it should set the need reset bit. >> The problem is that we can't depend on the device. If it takes too >> long for the device to respond to cvq, there's a high possibility that >> the device is buggy or even malicious. We can have a higher timeout >> here and it should be still better than waiting forever (the cvq >> commands need to be serialized so it needs to hold a lock anyway >> (RTNL) ). >> >> Thanks > With a TODO item like this I'd expect this to be an RFC. > Here's why: > > Making driver more robust from device failures is a laudable goal but it's really > hard to be 100% foolproof here. E.g. device can just block pci reads and > it would be very hard to recover.
Yes.
> So I'm going to only merge patches > like this if they at least theoretically have very little chance > of breaking existing users.
AFAIK, this is not theoretical, consider:
1) DPU may implement virtio-net CVQ with codes running in CPU 2) VDUSE may want to support CVQ in the future
> > And note that in most setups, CVQ is only used at startup and then left mostly alone. > > Finally, note that lots of guests need virtio to do anything useful at all. > So just failing commands is not enough to recover - you need to try > harder maybe by attempting to reset device.
This requires upper layer support which seems not existed in the networking subsystem.
> Could be a question of > policy - might need to make this guest configurable.
Yes.
Thanks
> > > >>> >>>> +} >>>> +EXPORT_SYMBOL_GPL(virtqueue_wait_for_used); >>>> + >>>> +void virtqueue_wake_up(struct virtqueue *_vq) >>>> +{ >>>> + struct vring_virtqueue *vq = to_vvq(_vq); >>>> + >>>> + wake_up_interruptible(&vq->wq); >>>> +} >>>> +EXPORT_SYMBOL_GPL(virtqueue_wake_up); >>>> + >>>> MODULE_LICENSE("GPL"); >>>> diff --git a/include/linux/virtio.h b/include/linux/virtio.h >>>> index dcab9c7e8784..2eb62c774895 100644 >>>> --- a/include/linux/virtio.h >>>> +++ b/include/linux/virtio.h >>>> @@ -72,6 +72,9 @@ void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len); >>>> void *virtqueue_get_buf_ctx(struct virtqueue *vq, unsigned int *len, >>>> void **ctx); >>>> >>>> +int virtqueue_wait_for_used(struct virtqueue *vq); >>>> +void virtqueue_wake_up(struct virtqueue *vq); >>>> + >>>> void virtqueue_disable_cb(struct virtqueue *vq); >>>> >>>> bool virtqueue_enable_cb(struct virtqueue *vq); >>>> -- >>>> 2.25.1
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