Jason Wang
2021-Feb-10 05:57 UTC
[RFC 09/10] vhost: Route guest->host notification through shadow virtqueue
On 2021/2/9 ??11:02, Eugenio Perez Martin wrote:> On Thu, Feb 4, 2021 at 4:27 AM Jason Wang <jasowang at redhat.com> wrote: >> >> On 2021/2/2 ??6:08, Eugenio Perez Martin wrote: >>> On Mon, Feb 1, 2021 at 7:29 AM Jason Wang <jasowang at redhat.com> wrote: >>>> On 2021/1/30 ??4:54, Eugenio P?rez wrote: >>>>> Shadow virtqueue notifications forwarding is disabled when vhost_dev >>>>> stops. >>>>> >>>>> Signed-off-by: Eugenio P?rez <eperezma at redhat.com> >>>>> --- >>>>> hw/virtio/vhost-shadow-virtqueue.h | 5 ++ >>>>> include/hw/virtio/vhost.h | 4 + >>>>> hw/virtio/vhost-shadow-virtqueue.c | 123 +++++++++++++++++++++++++- >>>>> hw/virtio/vhost.c | 135 ++++++++++++++++++++++++++++- >>>>> 4 files changed, 264 insertions(+), 3 deletions(-) >>>>> >>>>> diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h >>>>> index 6cc18d6acb..466f8ae595 100644 >>>>> --- a/hw/virtio/vhost-shadow-virtqueue.h >>>>> +++ b/hw/virtio/vhost-shadow-virtqueue.h >>>>> @@ -17,6 +17,11 @@ >>>>> >>>>> typedef struct VhostShadowVirtqueue VhostShadowVirtqueue; >>>>> >>>>> +bool vhost_shadow_vq_start_rcu(struct vhost_dev *dev, >>>>> + VhostShadowVirtqueue *svq); >>>>> +void vhost_shadow_vq_stop_rcu(struct vhost_dev *dev, >>>>> + VhostShadowVirtqueue *svq); >>>>> + >>>>> VhostShadowVirtqueue *vhost_shadow_vq_new(struct vhost_dev *dev, int idx); >>>>> >>>>> void vhost_shadow_vq_free(VhostShadowVirtqueue *vq); >>>>> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h >>>>> index 2be782cefd..732a4b2a2b 100644 >>>>> --- a/include/hw/virtio/vhost.h >>>>> +++ b/include/hw/virtio/vhost.h >>>>> @@ -55,6 +55,8 @@ struct vhost_iommu { >>>>> QLIST_ENTRY(vhost_iommu) iommu_next; >>>>> }; >>>>> >>>>> +typedef struct VhostShadowVirtqueue VhostShadowVirtqueue; >>>>> + >>>>> typedef struct VhostDevConfigOps { >>>>> /* Vhost device config space changed callback >>>>> */ >>>>> @@ -83,7 +85,9 @@ struct vhost_dev { >>>>> uint64_t backend_cap; >>>>> bool started; >>>>> bool log_enabled; >>>>> + bool sw_lm_enabled; >>>>> uint64_t log_size; >>>>> + VhostShadowVirtqueue **shadow_vqs; >>>>> Error *migration_blocker; >>>>> const VhostOps *vhost_ops; >>>>> void *opaque; >>>>> diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c >>>>> index c0c967a7c5..908c36c66d 100644 >>>>> --- a/hw/virtio/vhost-shadow-virtqueue.c >>>>> +++ b/hw/virtio/vhost-shadow-virtqueue.c >>>>> @@ -8,15 +8,129 @@ >>>>> */ >>>>> >>>>> #include "hw/virtio/vhost-shadow-virtqueue.h" >>>>> +#include "hw/virtio/vhost.h" >>>>> +#include "hw/virtio/virtio-access.h" >>>>> + >>>>> +#include "standard-headers/linux/vhost_types.h" >>>>> +#include "standard-headers/linux/virtio_ring.h" >>>>> >>>>> #include "qemu/error-report.h" >>>>> -#include "qemu/event_notifier.h" >>>>> +#include "qemu/main-loop.h" >>>>> >>>>> typedef struct VhostShadowVirtqueue { >>>>> EventNotifier kick_notifier; >>>>> EventNotifier call_notifier; >>>>> + const struct vhost_virtqueue *hvq; >>>>> + VirtIODevice *vdev; >>>>> + VirtQueue *vq; >>>>> } VhostShadowVirtqueue; >>>> So instead of doing things at virtio level, how about do the shadow >>>> stuffs at vhost level? >>>> >>>> It works like: >>>> >>>> virtio -> [shadow vhost backend] -> vhost backend >>>> >>>> Then the QMP is used to plug the shadow vhost backend in the middle or not. >>>> >>>> It looks kind of easier since we don't need to deal with virtqueue >>>> handlers etc.. Instead, we just need to deal with eventfd stuffs: >>>> >>>> When shadow vhost mode is enabled, we just intercept the host_notifiers >>>> and guest_notifiers. When it was disabled, we just pass the host/guest >>>> notifiers to the real vhost backends? >>>> >>> Hi Jason. >>> >>> Sure we can try that model, but it seems to me that it comes with a >>> different set of problems. >>> >>> For example, there are code in vhost.c that checks if implementations >>> are available in vhost_ops, like: >>> >>> if (dev->vhost_ops->vhost_vq_get_addr) { >>> r = dev->vhost_ops->vhost_vq_get_addr(dev, &addr, vq); >>> ... >>> } >>> >>> I can count 14 of these, checking: >>> >>> dev->vhost_ops->vhost_backend_can_merge >>> dev->vhost_ops->vhost_backend_mem_section_filter >>> dev->vhost_ops->vhost_force_iommu >>> dev->vhost_ops->vhost_requires_shm_log >>> dev->vhost_ops->vhost_set_backend_cap >>> dev->vhost_ops->vhost_set_vring_busyloop_timeout >>> dev->vhost_ops->vhost_vq_get_addr >>> hdev->vhost_ops->vhost_dev_start >>> hdev->vhost_ops->vhost_get_config >>> hdev->vhost_ops->vhost_get_inflight_fd >>> hdev->vhost_ops->vhost_net_set_backend >>> hdev->vhost_ops->vhost_set_config >>> hdev->vhost_ops->vhost_set_inflight_fd >>> hdev->vhost_ops->vhost_set_iotlb_callback >>> >>> So we should Implement all of the vhost_ops callbacks, forwarding them >>> to actual vhost_backed, and delete conditionally these ones? In other >>> words, dynamically generate the new shadow vq vhost_ops? If a new >>> callback is added to any vhost backend in the future, do we have to >>> force the adding / checking for NULL in shadow backend vhost_ops? >>> Would this be a good moment to check if all backends implement these >>> and delete the checks? >> >> I think it won't be easy if we want to support all kinds of vhost >> backends from the start. So we can go with vhost-vdpa one first. >> >> Actually how it work might be something like (no need to switch >> vhost_ops, we can do everything silently in the ops) >> >> 1) when device to switch to shadow vq (e.g via QMP) >> 2) vhost-vdpa will stop and sync state (last_avail_idx) internally >> 3) reset vhost-vdpa, clean call and kick eventfd >> 4) allocate vqs for vhost-vdpa, new call and kick eventfd, restart >> vhost-vdpa >> 5) start the shadow vq (make it start for last_avail_idx) >> 6) intercept ioeventfd and forward the request to callfd >> 7) intercept callfd and forward the request to irqfd >> 8) forward request between shadow virtqueue and vhost-vdpa >> > Sorry, still not clear to me how it relates with the actual backend used :).So I think I meant is, if we're doing at vhost level, we only play with eventfds not the event notifiers abstraction in virtio level.> > Would it work for you if we finish the notifications forwarding part > and we work on the buffer forwarding part?I think it's better to do them all since the notification forward itself is not a complete fnction.> > I'm going to send another cleaner revision, with less dependencies on > virtio code, only notifications eventfds. I think it will be easier to > discuss the changes on top of that.Right, let's discuss there. Thanks> >>> There are also checks like: >>> >>> if (dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER) >>> >>> How would shadow_vq backend expose itself? (I guess as the actual used backend). >>> >>> I can modify this patchset to not relay the guest->host notifications >>> on vq handlers but on eventfd handlers. Although this will make it >>> independent of the actual virtio device kind used, I can see two >>> drawbacks: >>> * The actual fact that it makes it independent of virtio device kind. >>> If a device does not use the notifiers and poll the ring by itself, it >>> has no chance of knowing that it should stop. What happens if >>> virtio-net tx timer is armed when we start shadow vq?. >> >> So if we do that in vhost level, it's a vhost backend from the virtio >> layer. Then we don't need to worry about tx timer stuffs. >> > Got it. > > So I'm going to assume that no device in virtio layer needs to be > aware of the change. It seems a valid assumption to me. > >>> * The fixes (current and future) in vq notifications, like the one >>> currently implemented in virtio_notify_irqfd for windows drivers >>> regarding ISR bit 0. I think this one in particular is OK not to >>> carry, but I think many changes affecting any of the functions will >>> have to be mirrored in the other. >> >> Consider we behave like a vhost, it just work as in the past for other >> type of vhost backends when MSI-X is not enabled? >> > Yes, it may be a bad example, as vhost devices may not update it. > However I still think a lot of features (packed ring buffers > treatment, etc), performance optimizations and future fixes will have > to apply to two different codes in case we roll our own buffers > treatment. > > Expanding in thread of patch 05/10, since you propose two solutions for this. > > Thanks! > > >> Thanks >> >> >>> Thoughts on this? >>> >>> Thanks! >>> >>>> Thanks >>>> >>>> >>>>> +static uint16_t vhost_shadow_vring_used_flags(VhostShadowVirtqueue *svq) >>>>> +{ >>>>> + const struct vring_used *used = svq->hvq->used; >>>>> + return virtio_tswap16(svq->vdev, used->flags); >>>>> +} >>>>> + >>>>> +static bool vhost_shadow_vring_should_kick(VhostShadowVirtqueue *vq) >>>>> +{ >>>>> + return !(vhost_shadow_vring_used_flags(vq) & VRING_USED_F_NO_NOTIFY); >>>>> +} >>>>> + >>>>> +static void vhost_shadow_vring_kick(VhostShadowVirtqueue *vq) >>>>> +{ >>>>> + if (vhost_shadow_vring_should_kick(vq)) { >>>>> + event_notifier_set(&vq->kick_notifier); >>>>> + } >>>>> +} >>>>> + >>>>> +static void handle_shadow_vq(VirtIODevice *vdev, VirtQueue *vq) >>>>> +{ >>>>> + struct vhost_dev *hdev = vhost_dev_from_virtio(vdev); >>>>> + uint16_t idx = virtio_get_queue_index(vq); >>>>> + >>>>> + VhostShadowVirtqueue *svq = hdev->shadow_vqs[idx]; >>>>> + >>>>> + vhost_shadow_vring_kick(svq); >>>>> +} >>>>> + >>>>> +/* >>>>> + * Start shadow virtqueue operation. >>>>> + * @dev vhost device >>>>> + * @svq Shadow Virtqueue >>>>> + * >>>>> + * Run in RCU context >>>>> + */ >>>>> +bool vhost_shadow_vq_start_rcu(struct vhost_dev *dev, >>>>> + VhostShadowVirtqueue *svq) >>>>> +{ >>>>> + const VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(dev->vdev); >>>>> + EventNotifier *vq_host_notifier = virtio_queue_get_host_notifier(svq->vq); >>>>> + unsigned idx = virtio_queue_get_idx(svq->vdev, svq->vq); >>>>> + struct vhost_vring_file kick_file = { >>>>> + .index = idx, >>>>> + .fd = event_notifier_get_fd(&svq->kick_notifier), >>>>> + }; >>>>> + int r; >>>>> + bool ok; >>>>> + >>>>> + /* Check that notifications are still going directly to vhost dev */ >>>>> + assert(virtio_queue_host_notifier_status(svq->vq)); >>>>> + >>>>> + ok = k->set_vq_handler(dev->vdev, idx, handle_shadow_vq); >>>>> + if (!ok) { >>>>> + error_report("Couldn't set the vq handler"); >>>>> + goto err_set_kick_handler; >>>>> + } >>>>> + >>>>> + r = dev->vhost_ops->vhost_set_vring_kick(dev, &kick_file); >>>>> + if (r != 0) { >>>>> + error_report("Couldn't set kick fd: %s", strerror(errno)); >>>>> + goto err_set_vring_kick; >>>>> + } >>>>> + >>>>> + event_notifier_set_handler(vq_host_notifier, >>>>> + virtio_queue_host_notifier_read); >>>>> + virtio_queue_set_host_notifier_enabled(svq->vq, false); >>>>> + virtio_queue_host_notifier_read(vq_host_notifier); >>>>> + >>>>> + return true; >>>>> + >>>>> +err_set_vring_kick: >>>>> + k->set_vq_handler(dev->vdev, idx, NULL); >>>>> + >>>>> +err_set_kick_handler: >>>>> + return false; >>>>> +} >>>>> + >>>>> +/* >>>>> + * Stop shadow virtqueue operation. >>>>> + * @dev vhost device >>>>> + * @svq Shadow Virtqueue >>>>> + * >>>>> + * Run in RCU context >>>>> + */ >>>>> +void vhost_shadow_vq_stop_rcu(struct vhost_dev *dev, >>>>> + VhostShadowVirtqueue *svq) >>>>> +{ >>>>> + const VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(svq->vdev); >>>>> + unsigned idx = virtio_queue_get_idx(svq->vdev, svq->vq); >>>>> + EventNotifier *vq_host_notifier = virtio_queue_get_host_notifier(svq->vq); >>>>> + struct vhost_vring_file kick_file = { >>>>> + .index = idx, >>>>> + .fd = event_notifier_get_fd(vq_host_notifier), >>>>> + }; >>>>> + int r; >>>>> + >>>>> + /* Restore vhost kick */ >>>>> + r = dev->vhost_ops->vhost_set_vring_kick(dev, &kick_file); >>>>> + /* Cannot do a lot of things */ >>>>> + assert(r == 0); >>>>> + >>>>> + event_notifier_set_handler(vq_host_notifier, NULL); >>>>> + virtio_queue_set_host_notifier_enabled(svq->vq, true); >>>>> + k->set_vq_handler(svq->vdev, idx, NULL); >>>>> +} >>>>> + >>>>> /* >>>>> * Creates vhost shadow virtqueue, and instruct vhost device to use the shadow >>>>> * methods and file descriptors. >>>>> @@ -24,8 +138,13 @@ typedef struct VhostShadowVirtqueue { >>>>> VhostShadowVirtqueue *vhost_shadow_vq_new(struct vhost_dev *dev, int idx) >>>>> { >>>>> g_autofree VhostShadowVirtqueue *svq = g_new0(VhostShadowVirtqueue, 1); >>>>> + int vq_idx = dev->vhost_ops->vhost_get_vq_index(dev, dev->vq_index + idx); >>>>> int r; >>>>> >>>>> + svq->vq = virtio_get_queue(dev->vdev, vq_idx); >>>>> + svq->hvq = &dev->vqs[idx]; >>>>> + svq->vdev = dev->vdev; >>>>> + >>>>> r = event_notifier_init(&svq->kick_notifier, 0); >>>>> if (r != 0) { >>>>> error_report("Couldn't create kick event notifier: %s", >>>>> @@ -40,7 +159,7 @@ VhostShadowVirtqueue *vhost_shadow_vq_new(struct vhost_dev *dev, int idx) >>>>> goto err_init_call_notifier; >>>>> } >>>>> >>>>> - return svq; >>>>> + return g_steal_pointer(&svq); >>>>> >>>>> err_init_call_notifier: >>>>> event_notifier_cleanup(&svq->kick_notifier); >>>>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c >>>>> index 42836e45f3..bde688f278 100644 >>>>> --- a/hw/virtio/vhost.c >>>>> +++ b/hw/virtio/vhost.c >>>>> @@ -25,6 +25,7 @@ >>>>> #include "exec/address-spaces.h" >>>>> #include "hw/virtio/virtio-bus.h" >>>>> #include "hw/virtio/virtio-access.h" >>>>> +#include "hw/virtio/vhost-shadow-virtqueue.h" >>>>> #include "migration/blocker.h" >>>>> #include "migration/qemu-file-types.h" >>>>> #include "sysemu/dma.h" >>>>> @@ -945,6 +946,82 @@ static void vhost_log_global_stop(MemoryListener *listener) >>>>> } >>>>> } >>>>> >>>>> +static int vhost_sw_live_migration_stop(struct vhost_dev *dev) >>>>> +{ >>>>> + int idx; >>>>> + >>>>> + WITH_RCU_READ_LOCK_GUARD() { >>>>> + dev->sw_lm_enabled = false; >>>>> + >>>>> + for (idx = 0; idx < dev->nvqs; ++idx) { >>>>> + vhost_shadow_vq_stop_rcu(dev, dev->shadow_vqs[idx]); >>>>> + } >>>>> + } >>>>> + >>>>> + for (idx = 0; idx < dev->nvqs; ++idx) { >>>>> + vhost_shadow_vq_free(dev->shadow_vqs[idx]); >>>>> + } >>>>> + >>>>> + g_free(dev->shadow_vqs); >>>>> + dev->shadow_vqs = NULL; >>>>> + return 0; >>>>> +} >>>>> + >>>>> +static int vhost_sw_live_migration_start(struct vhost_dev *dev) >>>>> +{ >>>>> + int idx; >>>>> + >>>>> + dev->shadow_vqs = g_new0(VhostShadowVirtqueue *, dev->nvqs); >>>>> + for (idx = 0; idx < dev->nvqs; ++idx) { >>>>> + dev->shadow_vqs[idx] = vhost_shadow_vq_new(dev, idx); >>>>> + if (unlikely(dev->shadow_vqs[idx] == NULL)) { >>>>> + goto err; >>>>> + } >>>>> + } >>>>> + >>>>> + WITH_RCU_READ_LOCK_GUARD() { >>>>> + for (idx = 0; idx < dev->nvqs; ++idx) { >>>>> + int stop_idx = idx; >>>>> + bool ok = vhost_shadow_vq_start_rcu(dev, >>>>> + dev->shadow_vqs[idx]); >>>>> + >>>>> + if (!ok) { >>>>> + while (--stop_idx >= 0) { >>>>> + vhost_shadow_vq_stop_rcu(dev, dev->shadow_vqs[stop_idx]); >>>>> + } >>>>> + >>>>> + goto err; >>>>> + } >>>>> + } >>>>> + } >>>>> + >>>>> + dev->sw_lm_enabled = true; >>>>> + return 0; >>>>> + >>>>> +err: >>>>> + for (; idx >= 0; --idx) { >>>>> + vhost_shadow_vq_free(dev->shadow_vqs[idx]); >>>>> + } >>>>> + g_free(dev->shadow_vqs[idx]); >>>>> + >>>>> + return -1; >>>>> +} >>>>> + >>>>> +static int vhost_sw_live_migration_enable(struct vhost_dev *dev, >>>>> + bool enable_lm) >>>>> +{ >>>>> + int r; >>>>> + >>>>> + if (enable_lm == dev->sw_lm_enabled) { >>>>> + return 0; >>>>> + } >>>>> + >>>>> + r = enable_lm ? vhost_sw_live_migration_start(dev) >>>>> + : vhost_sw_live_migration_stop(dev); >>>>> + >>>>> + return r; >>>>> +} >>>>> + >>>>> static void vhost_log_start(MemoryListener *listener, >>>>> MemoryRegionSection *section, >>>>> int old, int new) >>>>> @@ -1389,6 +1466,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque, >>>>> hdev->log = NULL; >>>>> hdev->log_size = 0; >>>>> hdev->log_enabled = false; >>>>> + hdev->sw_lm_enabled = false; >>>>> hdev->started = false; >>>>> memory_listener_register(&hdev->memory_listener, &address_space_memory); >>>>> QLIST_INSERT_HEAD(&vhost_devices, hdev, entry); >>>>> @@ -1816,6 +1894,11 @@ void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev) >>>>> hdev->vhost_ops->vhost_dev_start(hdev, false); >>>>> } >>>>> for (i = 0; i < hdev->nvqs; ++i) { >>>>> + if (hdev->sw_lm_enabled) { >>>>> + vhost_shadow_vq_stop_rcu(hdev, hdev->shadow_vqs[i]); >>>>> + vhost_shadow_vq_free(hdev->shadow_vqs[i]); >>>>> + } >>>>> + >>>>> vhost_virtqueue_stop(hdev, >>>>> vdev, >>>>> hdev->vqs + i, >>>>> @@ -1829,6 +1912,8 @@ void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev) >>>>> memory_listener_unregister(&hdev->iommu_listener); >>>>> } >>>>> vhost_log_put(hdev, true); >>>>> + g_free(hdev->shadow_vqs); >>>>> + hdev->sw_lm_enabled = false; >>>>> hdev->started = false; >>>>> hdev->vdev = NULL; >>>>> } >>>>> @@ -1845,5 +1930,53 @@ int vhost_net_set_backend(struct vhost_dev *hdev, >>>>> >>>>> void qmp_x_vhost_enable_shadow_vq(const char *name, bool enable, Error **errp) >>>>> { >>>>> - error_setg(errp, "Shadow virtqueue still not implemented."); >>>>> + struct vhost_dev *hdev; >>>>> + const char *err_cause = NULL; >>>>> + const VirtioDeviceClass *k; >>>>> + int r; >>>>> + ErrorClass err_class = ERROR_CLASS_GENERIC_ERROR; >>>>> + >>>>> + QLIST_FOREACH(hdev, &vhost_devices, entry) { >>>>> + if (hdev->vdev && 0 == strcmp(hdev->vdev->name, name)) { >>>>> + break; >>>>> + } >>>>> + } >>>>> + >>>>> + if (!hdev) { >>>>> + err_class = ERROR_CLASS_DEVICE_NOT_FOUND; >>>>> + err_cause = "Device not found"; >>>>> + goto err; >>>>> + } >>>>> + >>>>> + if (!hdev->started) { >>>>> + err_cause = "Device is not started"; >>>>> + goto err; >>>>> + } >>>>> + >>>>> + if (hdev->acked_features & BIT_ULL(VIRTIO_F_RING_PACKED)) { >>>>> + err_cause = "Use packed vq"; >>>>> + goto err; >>>>> + } >>>>> + >>>>> + if (vhost_dev_has_iommu(hdev)) { >>>>> + err_cause = "Device use IOMMU"; >>>>> + goto err; >>>>> + } >>>>> + >>>>> + k = VIRTIO_DEVICE_GET_CLASS(hdev->vdev); >>>>> + if (!k->set_vq_handler) { >>>>> + err_cause = "Virtio device type does not support reset of vq handler"; >>>>> + goto err; >>>>> + } >>>>> + >>>>> + r = vhost_sw_live_migration_enable(hdev, enable); >>>>> + if (unlikely(r)) { >>>>> + err_cause = "Error enabling (see monitor)"; >>>>> + } >>>>> + >>>>> +err: >>>>> + if (err_cause) { >>>>> + error_set(errp, err_class, >>>>> + "Can't enable shadow vq on %s: %s", name, err_cause); >>>>> + } >>>>> } >