Messages in this thread Patch in this message | | | Date | Fri, 19 Jan 2018 11:44:21 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v22 2/3] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ |
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On 01/18/2018 12:44 AM, Michael S. Tsirkin wrote: > On Wed, Jan 17, 2018 at 01:10:11PM +0800, Wei Wang wrote: >
> >> +{ >> + struct scatterlist sg; >> + unsigned int unused; >> + int err; >> + >> + sg_init_one(&sg, addr, sizeof(uint32_t)); > This passes a guest-endian value to host. This is a problem: > should always pass LE values.
I think the endianness is handled when virtqueue_add_outbuf():
desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
right?
> >> + >> + /* >> + * This handles the cornercase that the vq happens to be full when >> + * adding a cmd id. Rarely happen in practice. >> + */ >> + while (!vq->num_free) >> + virtqueue_get_buf(vq, &unused); > I dislike this busy-waiting. It's a hint after all - > why not just retry later - hopefully after getting an > interrupt? > > Alternatively, stop adding more entries when we have a single > ring entry left, making sure we have space for the command.
I think the second one looks good. Thanks.
>> + queue_work(system_freezable_wq, >> + &vb->update_balloon_size_work); >> + spin_unlock_irqrestore(&vb->stop_update_lock, flags); >> + } >> + >> + virtio_cread(vb->vdev, struct virtio_balloon_config, >> + free_page_report_cmd_id, &cmd_id); > You want virtio_cread_feature, don't access the new field > if the feature has not been negotiated.
Right. We probably need to put all the following cmd id related things under the feature check,
How about
if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ)) { virtio_cread(..); if (cmd_id == VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID) { .... }
> > >> + if (cmd_id == VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID) { >> + WRITE_ONCE(vb->report_free_page, false); >> + } else if (cmd_id != vb->start_cmd_id) { >> + /* >> + * Host requests to start the reporting by sending a new cmd >> + * id. >> + */ >> + WRITE_ONCE(vb->report_free_page, true); > I don't know why we bother with WRITE_ONCE here. The point of > report_free_page being used lockless is that that it's not a big deal if > it's wrong occasionally, right?
Actually the main reason is that "vb->report_free_page" is a value shared by two threads: Written by the config_change here, and read by the worker thread that reports the free pages.
Alternatively, we could let the two sides access to the shared variable with "volatile" pointers.
> > > >> + vb->start_cmd_id = cmd_id; >> + queue_work(vb->balloon_wq, &vb->report_free_page_work); > It seems that if a command was already queued (with a different id), > this will result in new command id being sent to host twice, which will > likely confuse the host.
I think that case won't happen, because - the host sends a cmd id to the guest via the config, while the guest acks back the received cmd id via the virtqueue; - the guest ack back a cmd id only when a new cmd id is received from the host, that is the above check:
if (cmd_id != vb->start_cmd_id) { --> the driver only queues the reporting work only when a new cmd id is received /* * Host requests to start the reporting by sending a * new cmd id. */ WRITE_ONCE(vb->report_free_page, true); vb->start_cmd_id = cmd_id; queue_work(vb->balloon_wq, &vb->report_free_page_work); }
So the same cmd id wouldn't queue the reporting work twice.
> > > >> + } >> +} >> + >> static void update_balloon_size(struct virtio_balloon *vb) >> { >> u32 actual = vb->num_pages; >> @@ -417,40 +513,113 @@ static void update_balloon_size_func(struct work_struct *work) >> >> static int init_vqs(struct virtio_balloon *vb) >> { >> - struct virtqueue *vqs[3]; >> - vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request }; >> - static const char * const names[] = { "inflate", "deflate", "stats" }; >> - int err, nvqs; >> + struct virtqueue **vqs; >> + vq_callback_t **callbacks; >> + const char **names; >> + struct scatterlist sg; >> + int i, nvqs, err = -ENOMEM; >> + >> + /* Inflateq and deflateq are used unconditionally */ >> + nvqs = 2; >> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) >> + nvqs++; >> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ)) >> + nvqs++; >> + >> + /* Allocate space for find_vqs parameters */ >> + vqs = kcalloc(nvqs, sizeof(*vqs), GFP_KERNEL); >> + if (!vqs) >> + goto err_vq; >> + callbacks = kmalloc_array(nvqs, sizeof(*callbacks), GFP_KERNEL); >> + if (!callbacks) >> + goto err_callback; >> + names = kmalloc_array(nvqs, sizeof(*names), GFP_KERNEL); >> + if (!names) >> + goto err_names; > Why not just keep these 3 arrays on stack? they aren't large.
Sounds good. Here is the new implementation:
static int init_vqs(struct virtio_balloon *vb) { struct virtqueue *vqs[4]; vq_callback_t *callbacks[4]; const char *names[4]; struct scatterlist sg; int ret;
/* * Inflateq and deflateq are used unconditionally. stats_vq and * free_page_vq uses names[2] and names[3], respectively. The names[] * will be NULL if the related feature is not enabled, which will * cause no allocation for the corresponding virtqueue in find_vqs. */ callbacks[0] = balloon_ack; names[0] = "inflate"; callbacks[1] = balloon_ack; names[1] = "deflate"; names[2] = NULL; names[3] = NULL;
if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { names[2] = "stats"; callbacks[2] = stats_request; } if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ)) { names[3] = "free_page_vq"; callbacks[3] = NULL; }
ret = vb->vdev->config->find_vqs(vb->vdev, 4, vqs, callbacks, names, NULL, NULL); if (ret) return ret;
vb->inflate_vq = vqs[0]; vb->deflate_vq = vqs[1];
if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { vb->stats_vq = vqs[2]; /* * Prime this virtqueue with one buffer so the hypervisor can * use it to signal us later (it can't be broken yet!). */ sg_init_one(&sg, vb->stats, sizeof(vb->stats)); ret = virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL); if (ret) { dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n", __func__); return ret; } virtqueue_kick(vb->stats_vq); } if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ)) vb->free_page_vq = vqs[3]; return 0; }
Btw, the QEMU side doesn't have an option to disable STATS_VQ currently, we may need to add that later.
Best, Wei
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