Jason Wang
2021-Mar-18 03:14 UTC
[RFC v2 11/13] vhost: Shadow virtqueue buffers forwarding
? 2021/3/17 ??10:38, Eugenio Perez Martin ??:> On Wed, Mar 17, 2021 at 3:51 AM Jason Wang <jasowang at redhat.com> wrote: >> >> ? 2021/3/17 ??12:05, Eugenio Perez Martin ??: >>> On Tue, Mar 16, 2021 at 9:15 AM Jason Wang <jasowang at redhat.com> wrote: >>>> ? 2021/3/16 ??3:48, Eugenio P?rez ??: >>>>> Initial version of shadow virtqueue that actually forward buffers. >>>>> >>>>> It reuses the VirtQueue code for the device part. The driver part is >>>>> based on Linux's virtio_ring driver, but with stripped functionality >>>>> and optimizations so it's easier to review. >>>>> >>>>> These will be added in later commits. >>>>> >>>>> Signed-off-by: Eugenio P?rez <eperezma at redhat.com> >>>>> --- >>>>> hw/virtio/vhost-shadow-virtqueue.c | 212 +++++++++++++++++++++++++++-- >>>>> hw/virtio/vhost.c | 113 ++++++++++++++- >>>>> 2 files changed, 312 insertions(+), 13 deletions(-) >>>>> >>>>> diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c >>>>> index 1460d1d5d1..68ed0f2740 100644 >>>>> --- a/hw/virtio/vhost-shadow-virtqueue.c >>>>> +++ b/hw/virtio/vhost-shadow-virtqueue.c >>>>> @@ -9,6 +9,7 @@ >>>>> >>>>> #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" >>>>> >>>>> @@ -55,11 +56,96 @@ typedef struct VhostShadowVirtqueue { >>>>> /* Virtio device */ >>>>> VirtIODevice *vdev; >>>>> >>>>> + /* Map for returning guest's descriptors */ >>>>> + VirtQueueElement **ring_id_maps; >>>>> + >>>>> + /* Next head to expose to device */ >>>>> + uint16_t avail_idx_shadow; >>>>> + >>>>> + /* Next free descriptor */ >>>>> + uint16_t free_head; >>>>> + >>>>> + /* Last seen used idx */ >>>>> + uint16_t shadow_used_idx; >>>>> + >>>>> + /* Next head to consume from device */ >>>>> + uint16_t used_idx; >>>>> + >>>>> /* Descriptors copied from guest */ >>>>> vring_desc_t descs[]; >>>>> } VhostShadowVirtqueue; >>>>> >>>>> -/* Forward guest notifications */ >>>>> +static void vhost_vring_write_descs(VhostShadowVirtqueue *svq, >>>>> + const struct iovec *iovec, >>>>> + size_t num, bool more_descs, bool write) >>>>> +{ >>>>> + uint16_t i = svq->free_head, last = svq->free_head; >>>>> + unsigned n; >>>>> + uint16_t flags = write ? virtio_tswap16(svq->vdev, VRING_DESC_F_WRITE) : 0; >>>>> + vring_desc_t *descs = svq->vring.desc; >>>>> + >>>>> + if (num == 0) { >>>>> + return; >>>>> + } >>>>> + >>>>> + for (n = 0; n < num; n++) { >>>>> + if (more_descs || (n + 1 < num)) { >>>>> + descs[i].flags = flags | virtio_tswap16(svq->vdev, >>>>> + VRING_DESC_F_NEXT); >>>>> + } else { >>>>> + descs[i].flags = flags; >>>>> + } >>>>> + descs[i].addr = virtio_tswap64(svq->vdev, (hwaddr)iovec[n].iov_base); >>>> So unsing virtio_tswap() is probably not correct since we're talking >>>> with vhost backends which has its own endiness. >>>> >>> I was trying to expose the buffer with the same endianness as the >>> driver originally offered, so if guest->qemu requires a bswap, I think >>> it will always require a bswap again to expose to the device again. >> >> So assumes vhost-vDPA always provide a non-transitional device[1]. >> >> Then if Qemu present a transitional device, we need to do the endian >> conversion when necessary, if Qemu present a non-transitional device, we >> don't need to do that, guest driver will do that for us. >> >> But it looks to me the virtio_tswap() can't be used for this since it: >> >> static inline bool virtio_access_is_big_endian(VirtIODevice *vdev) >> { >> #if defined(LEGACY_VIRTIO_IS_BIENDIAN) >> return virtio_is_big_endian(vdev); >> #elif defined(TARGET_WORDS_BIGENDIAN) >> if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) { >> /* Devices conforming to VIRTIO 1.0 or later are always LE. */ >> return false; >> } >> return true; >> #else >> return false; >> #endif >> } >> >> So if we present a legacy device on top of a non-transitiaonl vDPA >> device. The VIRITIO_F_VERSION_1 check is wrong. >> >> >>>> For vhost-vDPA, we can assume that it's a 1.0 device. >>> Isn't it needed if the host is big endian? >> >> [1] >> >> So non-transitional device always assume little endian. >> >> For vhost-vDPA, we don't want to present transitional device which may >> end up with a lot of burdens. >> >> I suspect the legacy driver plust vhost vDPA already break, so I plan to >> mandate VERSION_1 for all vDPA devices. >> > Right. I think it's the best then. > > However, then we will need a similar method to always expose > address/length as little endian, isn't it?Yes.> >>>>> + descs[i].len = virtio_tswap32(svq->vdev, iovec[n].iov_len); >>>>> + >>>>> + last = i; >>>>> + i = virtio_tswap16(svq->vdev, descs[i].next); >>>>> + } >>>>> + >>>>> + svq->free_head = virtio_tswap16(svq->vdev, descs[last].next); >>>>> +} >>>>> + >>>>> +static unsigned vhost_shadow_vq_add_split(VhostShadowVirtqueue *svq, >>>>> + VirtQueueElement *elem) >>>>> +{ >>>>> + int head; >>>>> + unsigned avail_idx; >>>>> + vring_avail_t *avail = svq->vring.avail; >>>>> + >>>>> + head = svq->free_head; >>>>> + >>>>> + /* We need some descriptors here */ >>>>> + assert(elem->out_num || elem->in_num); >>>>> + >>>>> + vhost_vring_write_descs(svq, elem->out_sg, elem->out_num, >>>>> + elem->in_num > 0, false); >>>>> + vhost_vring_write_descs(svq, elem->in_sg, elem->in_num, false, true); >>>>> + >>>>> + /* >>>>> + * Put entry in available array (but don't update avail->idx until they >>>>> + * do sync). >>>>> + */ >>>>> + avail_idx = svq->avail_idx_shadow & (svq->vring.num - 1); >>>>> + avail->ring[avail_idx] = virtio_tswap16(svq->vdev, head); >>>>> + svq->avail_idx_shadow++; >>>>> + >>>>> + /* Expose descriptors to device */ >>>>> + smp_wmb(); >>>>> + avail->idx = virtio_tswap16(svq->vdev, svq->avail_idx_shadow); >>>>> + >>>>> + return head; >>>>> + >>>>> +} >>>>> + >>>>> +static void vhost_shadow_vq_add(VhostShadowVirtqueue *svq, >>>>> + VirtQueueElement *elem) >>>>> +{ >>>>> + unsigned qemu_head = vhost_shadow_vq_add_split(svq, elem); >>>>> + >>>>> + svq->ring_id_maps[qemu_head] = elem; >>>>> +} >>>>> + >>>>> +/* Handle guest->device notifications */ >>>>> static void vhost_handle_guest_kick(EventNotifier *n) >>>>> { >>>>> VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue, >>>>> @@ -69,7 +155,72 @@ static void vhost_handle_guest_kick(EventNotifier *n) >>>>> return; >>>>> } >>>>> >>>>> - event_notifier_set(&svq->kick_notifier); >>>>> + /* Make available as many buffers as possible */ >>>>> + do { >>>>> + if (virtio_queue_get_notification(svq->vq)) { >>>>> + /* No more notifications until process all available */ >>>>> + virtio_queue_set_notification(svq->vq, false); >>>>> + } >>>>> + >>>>> + while (true) { >>>>> + VirtQueueElement *elem; >>>>> + if (virtio_queue_full(svq->vq)) { >>>>> + break; >>>> So we've disabled guest notification. If buffer has been consumed, we >>>> need to retry the handle_guest_kick here. But I didn't find the code? >>>> >>> This code follows the pattern of virtio_blk_handle_vq: we jump out of >>> the inner while, and we re-enable the notifications. After that, we >>> check for updates on guest avail_idx. >> >> Ok, but this will end up with a lot of unnecessary kicks without event >> index. >> > I can move the kick out of the inner loop, but that could add latency.So I think the right way is to disable the notification until some buffers are consumed by used ring.> >>>>> + } >>>>> + >>>>> + elem = virtqueue_pop(svq->vq, sizeof(*elem)); >>>>> + if (!elem) { >>>>> + break; >>>>> + } >>>>> + >>>>> + vhost_shadow_vq_add(svq, elem); >>>>> + event_notifier_set(&svq->kick_notifier); >>>>> + } >>>>> + >>>>> + virtio_queue_set_notification(svq->vq, true); >>>>> + } while (!virtio_queue_empty(svq->vq)); >>>>> +} >>>>> + >>>>> +static bool vhost_shadow_vq_more_used(VhostShadowVirtqueue *svq) >>>>> +{ >>>>> + if (svq->used_idx != svq->shadow_used_idx) { >>>>> + return true; >>>>> + } >>>>> + >>>>> + /* Get used idx must not be reordered */ >>>>> + smp_rmb(); >>>>> + svq->shadow_used_idx = virtio_tswap16(svq->vdev, svq->vring.used->idx); >>>>> + >>>>> + return svq->used_idx != svq->shadow_used_idx; >>>>> +} >>>>> + >>>>> +static VirtQueueElement *vhost_shadow_vq_get_buf(VhostShadowVirtqueue *svq) >>>>> +{ >>>>> + vring_desc_t *descs = svq->vring.desc; >>>>> + const vring_used_t *used = svq->vring.used; >>>>> + vring_used_elem_t used_elem; >>>>> + uint16_t last_used; >>>>> + >>>>> + if (!vhost_shadow_vq_more_used(svq)) { >>>>> + return NULL; >>>>> + } >>>>> + >>>>> + last_used = svq->used_idx & (svq->vring.num - 1); >>>>> + used_elem.id = virtio_tswap32(svq->vdev, used->ring[last_used].id); >>>>> + used_elem.len = virtio_tswap32(svq->vdev, used->ring[last_used].len); >>>>> + >>>>> + if (unlikely(used_elem.id >= svq->vring.num)) { >>>>> + error_report("Device %s says index %u is available", svq->vdev->name, >>>>> + used_elem.id); >>>>> + return NULL; >>>>> + } >>>>> + >>>>> + descs[used_elem.id].next = svq->free_head; >>>>> + svq->free_head = used_elem.id; >>>>> + >>>>> + svq->used_idx++; >>>>> + svq->ring_id_maps[used_elem.id]->len = used_elem.len; >>>>> + return g_steal_pointer(&svq->ring_id_maps[used_elem.id]); >>>>> } >>>>> >>>>> /* Forward vhost notifications */ >>>>> @@ -78,6 +229,7 @@ static void vhost_shadow_vq_handle_call_no_test(EventNotifier *n) >>>>> VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue, >>>>> call_notifier); >>>>> EventNotifier *masked_notifier; >>>>> + VirtQueue *vq = svq->vq; >>>>> >>>>> /* Signal start of using masked notifier */ >>>>> qemu_event_reset(&svq->masked_notifier.is_free); >>>>> @@ -86,14 +238,29 @@ static void vhost_shadow_vq_handle_call_no_test(EventNotifier *n) >>>>> qemu_event_set(&svq->masked_notifier.is_free); >>>>> } >>>>> >>>>> - if (!masked_notifier) { >>>>> - unsigned n = virtio_get_queue_index(svq->vq); >>>>> - virtio_queue_invalidate_signalled_used(svq->vdev, n); >>>>> - virtio_notify_irqfd(svq->vdev, svq->vq); >>>>> - } else if (!svq->masked_notifier.signaled) { >>>>> - svq->masked_notifier.signaled = true; >>>>> - event_notifier_set(svq->masked_notifier.n); >>>>> - } >>>>> + /* Make as many buffers as possible used. */ >>>>> + do { >>>>> + unsigned i = 0; >>>>> + >>>>> + /* TODO: Use VRING_AVAIL_F_NO_INTERRUPT */ >>>>> + while (true) { >>>>> + g_autofree VirtQueueElement *elem = vhost_shadow_vq_get_buf(svq); >>>>> + if (!elem) { >>>>> + break; >>>>> + } >>>>> + >>>>> + assert(i < svq->vring.num); >>>>> + virtqueue_fill(vq, elem, elem->len, i++); >>>>> + } >>>>> + >>>>> + virtqueue_flush(vq, i); >>>>> + if (!masked_notifier) { >>>>> + virtio_notify_irqfd(svq->vdev, svq->vq); >>>>> + } else if (!svq->masked_notifier.signaled) { >>>>> + svq->masked_notifier.signaled = true; >>>>> + event_notifier_set(svq->masked_notifier.n); >>>>> + } >>>>> + } while (vhost_shadow_vq_more_used(svq)); >>>>> >>>>> if (masked_notifier) { >>>>> /* Signal not using it anymore */ >>>>> @@ -103,7 +270,6 @@ static void vhost_shadow_vq_handle_call_no_test(EventNotifier *n) >>>>> >>>>> static void vhost_shadow_vq_handle_call(EventNotifier *n) >>>>> { >>>>> - >>>>> if (likely(event_notifier_test_and_clear(n))) { >>>>> vhost_shadow_vq_handle_call_no_test(n); >>>>> } >>>>> @@ -254,7 +420,11 @@ void vhost_shadow_vq_stop(struct vhost_dev *dev, >>>>> unsigned idx, >>>>> VhostShadowVirtqueue *svq) >>>>> { >>>>> + int i; >>>>> int r = vhost_shadow_vq_restore_vdev_host_notifier(dev, idx, svq); >>>>> + >>>>> + assert(!dev->shadow_vqs_enabled); >>>>> + >>>>> if (unlikely(r < 0)) { >>>>> error_report("Couldn't restore vq kick fd: %s", strerror(-r)); >>>>> } >>>>> @@ -272,6 +442,18 @@ void vhost_shadow_vq_stop(struct vhost_dev *dev, >>>>> /* Restore vhost call */ >>>>> vhost_virtqueue_mask(dev, dev->vdev, dev->vq_index + idx, >>>>> dev->vqs[idx].notifier_is_masked); >>>>> + >>>>> + >>>>> + for (i = 0; i < svq->vring.num; ++i) { >>>>> + g_autofree VirtQueueElement *elem = svq->ring_id_maps[i]; >>>>> + /* >>>>> + * Although the doc says we must unpop in order, it's ok to unpop >>>>> + * everything. >>>>> + */ >>>>> + if (elem) { >>>>> + virtqueue_unpop(svq->vq, elem, elem->len); >>>> Shouldn't we need to wait until all pending requests to be drained? Or >>>> we may end up duplicated requests? >>>> >>> Do you mean pending as in-flight/processing in the device? The device >>> must be paused at this point. >> >> Ok. I see there's a vhost_set_vring_enable(dev, false) in >> vhost_sw_live_migration_start(). >> >> >>> Currently there is no assertion for >>> this, maybe we can track the device status for it. >>> >>> For the queue handlers to be running at this point, the main event >>> loop should serialize QMP and handlers as far as I know (and they >>> would make all state inconsistent if the device stops suddenly). It >>> would need to be synchronized if the handlers run in their own AIO >>> context. That would be nice to have but it's not included here. >> >> That's why I suggest to just drop the QMP stuffs and use cli parameters >> to enable shadow virtqueue. Things would be greatly simplified I guess. >> > I can send a series without it, but SVQ will need to be able to kick > in dynamically sooner or later if we want to use it for live > migration.I'm not sure I get the issue here. My understnading is everyhing will be processed in the same aio context. Thanks> >> Thanks >> >> >>>> Thanks >>>> >>>> >>>>> + } >>>>> + } >>>>> } >>>>> >>>>> /* >>>>> @@ -284,7 +466,7 @@ VhostShadowVirtqueue *vhost_shadow_vq_new(struct vhost_dev *dev, int idx) >>>>> unsigned num = virtio_queue_get_num(dev->vdev, vq_idx); >>>>> size_t ring_size = vring_size(num, VRING_DESC_ALIGN_SIZE); >>>>> g_autofree VhostShadowVirtqueue *svq = g_malloc0(sizeof(*svq) + ring_size); >>>>> - int r; >>>>> + int r, i; >>>>> >>>>> r = event_notifier_init(&svq->kick_notifier, 0); >>>>> if (r != 0) { >>>>> @@ -303,6 +485,11 @@ VhostShadowVirtqueue *vhost_shadow_vq_new(struct vhost_dev *dev, int idx) >>>>> vring_init(&svq->vring, num, svq->descs, VRING_DESC_ALIGN_SIZE); >>>>> svq->vq = virtio_get_queue(dev->vdev, vq_idx); >>>>> svq->vdev = dev->vdev; >>>>> + for (i = 0; i < num - 1; i++) { >>>>> + svq->descs[i].next = virtio_tswap16(dev->vdev, i + 1); >>>>> + } >>>>> + >>>>> + svq->ring_id_maps = g_new0(VirtQueueElement *, num); >>>>> event_notifier_set_handler(&svq->call_notifier, >>>>> vhost_shadow_vq_handle_call); >>>>> qemu_event_init(&svq->masked_notifier.is_free, true); >>>>> @@ -324,5 +511,6 @@ void vhost_shadow_vq_free(VhostShadowVirtqueue *vq) >>>>> event_notifier_cleanup(&vq->kick_notifier); >>>>> event_notifier_set_handler(&vq->call_notifier, NULL); >>>>> event_notifier_cleanup(&vq->call_notifier); >>>>> + g_free(vq->ring_id_maps); >>>>> g_free(vq); >>>>> } >>>>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c >>>>> index eab3e334f2..a373999bc4 100644 >>>>> --- a/hw/virtio/vhost.c >>>>> +++ b/hw/virtio/vhost.c >>>>> @@ -1021,6 +1021,19 @@ int vhost_device_iotlb_miss(struct vhost_dev *dev, uint64_t iova, int write) >>>>> >>>>> trace_vhost_iotlb_miss(dev, 1); >>>>> >>>>> + if (qatomic_load_acquire(&dev->shadow_vqs_enabled)) { >>>>> + uaddr = iova; >>>>> + len = 4096; >>>>> + ret = vhost_backend_update_device_iotlb(dev, iova, uaddr, len, >>>>> + IOMMU_RW); >>>>> + if (ret) { >>>>> + trace_vhost_iotlb_miss(dev, 2); >>>>> + error_report("Fail to update device iotlb"); >>>>> + } >>>>> + >>>>> + return ret; >>>>> + } >>>>> + >>>>> iotlb = address_space_get_iotlb_entry(dev->vdev->dma_as, >>>>> iova, write, >>>>> MEMTXATTRS_UNSPECIFIED); >>>>> @@ -1227,8 +1240,28 @@ static int vhost_sw_live_migration_stop(struct vhost_dev *dev) >>>>> /* Can be read by vhost_virtqueue_mask, from vm exit */ >>>>> qatomic_store_release(&dev->shadow_vqs_enabled, false); >>>>> >>>>> + dev->vhost_ops->vhost_set_vring_enable(dev, false); >>>>> + if (vhost_backend_invalidate_device_iotlb(dev, 0, -1ULL)) { >>>>> + error_report("Fail to invalidate device iotlb"); >>>>> + } >>>>> + >>>>> for (idx = 0; idx < dev->nvqs; ++idx) { >>>>> + /* >>>>> + * Update used ring information for IOTLB to work correctly, >>>>> + * vhost-kernel code requires for this. >>>>> + */ >>>>> + struct vhost_virtqueue *vq = dev->vqs + idx; >>>>> + vhost_device_iotlb_miss(dev, vq->used_phys, true); >>>>> + >>>>> vhost_shadow_vq_stop(dev, idx, dev->shadow_vqs[idx]); >>>>> + vhost_virtqueue_start(dev, dev->vdev, &dev->vqs[idx], >>>>> + dev->vq_index + idx); >>>>> + } >>>>> + >>>>> + /* Enable guest's vq vring */ >>>>> + dev->vhost_ops->vhost_set_vring_enable(dev, true); >>>>> + >>>>> + for (idx = 0; idx < dev->nvqs; ++idx) { >>>>> vhost_shadow_vq_free(dev->shadow_vqs[idx]); >>>>> } >>>>> >>>>> @@ -1237,6 +1270,59 @@ static int vhost_sw_live_migration_stop(struct vhost_dev *dev) >>>>> return 0; >>>>> } >>>>> >>>>> +/* >>>>> + * Start shadow virtqueue in a given queue. >>>>> + * In failure case, this function leaves queue working as regular vhost mode. >>>>> + */ >>>>> +static bool vhost_sw_live_migration_start_vq(struct vhost_dev *dev, >>>>> + unsigned idx) >>>>> +{ >>>>> + struct vhost_vring_addr addr = { >>>>> + .index = idx, >>>>> + }; >>>>> + struct vhost_vring_state s = { >>>>> + .index = idx, >>>>> + }; >>>>> + int r; >>>>> + bool ok; >>>>> + >>>>> + vhost_virtqueue_stop(dev, dev->vdev, &dev->vqs[idx], dev->vq_index + idx); >>>>> + ok = vhost_shadow_vq_start(dev, idx, dev->shadow_vqs[idx]); >>>>> + if (unlikely(!ok)) { >>>>> + return false; >>>>> + } >>>>> + >>>>> + /* From this point, vhost_virtqueue_start can reset these changes */ >>>>> + vhost_shadow_vq_get_vring_addr(dev->shadow_vqs[idx], &addr); >>>>> + r = dev->vhost_ops->vhost_set_vring_addr(dev, &addr); >>>>> + if (unlikely(r != 0)) { >>>>> + VHOST_OPS_DEBUG("vhost_set_vring_addr for shadow vq failed"); >>>>> + goto err; >>>>> + } >>>>> + >>>>> + r = dev->vhost_ops->vhost_set_vring_base(dev, &s); >>>>> + if (unlikely(r != 0)) { >>>>> + VHOST_OPS_DEBUG("vhost_set_vring_base for shadow vq failed"); >>>>> + goto err; >>>>> + } >>>>> + >>>>> + /* >>>>> + * Update used ring information for IOTLB to work correctly, >>>>> + * vhost-kernel code requires for this. >>>>> + */ >>>>> + r = vhost_device_iotlb_miss(dev, addr.used_user_addr, true); >>>>> + if (unlikely(r != 0)) { >>>>> + /* Debug message already printed */ >>>>> + goto err; >>>>> + } >>>>> + >>>>> + return true; >>>>> + >>>>> +err: >>>>> + vhost_virtqueue_start(dev, dev->vdev, &dev->vqs[idx], dev->vq_index + idx); >>>>> + return false; >>>>> +} >>>>> + >>>>> static int vhost_sw_live_migration_start(struct vhost_dev *dev) >>>>> { >>>>> int idx, stop_idx; >>>>> @@ -1249,24 +1335,35 @@ static int vhost_sw_live_migration_start(struct vhost_dev *dev) >>>>> } >>>>> } >>>>> >>>>> + dev->vhost_ops->vhost_set_vring_enable(dev, false); >>>>> + if (vhost_backend_invalidate_device_iotlb(dev, 0, -1ULL)) { >>>>> + error_report("Fail to invalidate device iotlb"); >>>>> + } >>>>> + >>>>> /* Can be read by vhost_virtqueue_mask, from vm exit */ >>>>> qatomic_store_release(&dev->shadow_vqs_enabled, true); >>>>> for (idx = 0; idx < dev->nvqs; ++idx) { >>>>> - bool ok = vhost_shadow_vq_start(dev, idx, dev->shadow_vqs[idx]); >>>>> + bool ok = vhost_sw_live_migration_start_vq(dev, idx); >>>>> if (unlikely(!ok)) { >>>>> goto err_start; >>>>> } >>>>> } >>>>> >>>>> + /* Enable shadow vq vring */ >>>>> + dev->vhost_ops->vhost_set_vring_enable(dev, true); >>>>> return 0; >>>>> >>>>> err_start: >>>>> qatomic_store_release(&dev->shadow_vqs_enabled, false); >>>>> for (stop_idx = 0; stop_idx < idx; stop_idx++) { >>>>> vhost_shadow_vq_stop(dev, idx, dev->shadow_vqs[stop_idx]); >>>>> + vhost_virtqueue_start(dev, dev->vdev, &dev->vqs[idx], >>>>> + dev->vq_index + stop_idx); >>>>> } >>>>> >>>>> err_new: >>>>> + /* Enable guest's vring */ >>>>> + dev->vhost_ops->vhost_set_vring_enable(dev, true); >>>>> for (idx = 0; idx < dev->nvqs; ++idx) { >>>>> vhost_shadow_vq_free(dev->shadow_vqs[idx]); >>>>> } >>>>> @@ -1970,6 +2067,20 @@ void qmp_x_vhost_enable_shadow_vq(const char *name, bool enable, Error **errp) >>>>> >>>>> if (!hdev->started) { >>>>> err_cause = "Device is not started"; >>>>> + } else if (!vhost_dev_has_iommu(hdev)) { >>>>> + err_cause = "Does not support iommu"; >>>>> + } else if (hdev->acked_features & BIT_ULL(VIRTIO_F_RING_PACKED)) { >>>>> + err_cause = "Is packed"; >>>>> + } else if (hdev->acked_features & BIT_ULL(VIRTIO_RING_F_EVENT_IDX)) { >>>>> + err_cause = "Have event idx"; >>>>> + } else if (hdev->acked_features & >>>>> + BIT_ULL(VIRTIO_RING_F_INDIRECT_DESC)) { >>>>> + err_cause = "Supports indirect descriptors"; >>>>> + } else if (!hdev->vhost_ops->vhost_set_vring_enable) { >>>>> + err_cause = "Cannot pause device"; >>>>> + } >>>>> + >>>>> + if (err_cause) { >>>>> goto err; >>>>> } >>>>>