Re: [PATCH 18/31] vhost: Shadow virtqueue buffers forwarding

[Eugenio Perez Martin]

On Sun, Jan 30, 2022 at 5:43 AM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 在 2022/1/22 上午4:27, Eugenio Pérez 写道:
> > Initial version of shadow virtqueue that actually forward buffers. There
> > is no iommu support at the moment, and that will be addressed in future
> > patches of this series. Since all vhost-vdpa devices use forced IOMMU,
> > this means that SVQ is not usable at this point of the series on any
> > device.
> >
> > For simplicity it only supports modern devices, that expects vring
> > in little endian, with split ring and no event idx or indirect
> > descriptors. Support for them will not be added in this series.
> >
> > 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.
> >
> > However, forwarding buffers have some particular pieces: One of the most
> > unexpected ones is that a guest's buffer can expand through more than
> > one descriptor in SVQ. While this is handled gracefully by qemu's
> > emulated virtio devices, it may cause unexpected SVQ queue full. This
> > patch also solves it by checking for this condition at both guest's
> > kicks and device's calls. The code may be more elegant in the future if
> > SVQ code runs in its own iocontext.
> >
> > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > ---
> >   hw/virtio/vhost-shadow-virtqueue.h |   2 +
> >   hw/virtio/vhost-shadow-virtqueue.c | 365 ++++++++++++++++++++++++++++-
> >   hw/virtio/vhost-vdpa.c             | 111 ++++++++-
> >   3 files changed, 462 insertions(+), 16 deletions(-)
> >
> > diff --git a/hw/virtio/vhost-shadow-virtqueue.h 
> > b/hw/virtio/vhost-shadow-virtqueue.h
> > index 39aef5ffdf..19c934af49 100644
> > --- a/hw/virtio/vhost-shadow-virtqueue.h
> > +++ b/hw/virtio/vhost-shadow-virtqueue.h
> > @@ -33,6 +33,8 @@ uint16_t vhost_svq_get_num(const VhostShadowVirtqueue 
> > *svq);
> >   size_t vhost_svq_driver_area_size(const VhostShadowVirtqueue *svq);
> >   size_t vhost_svq_device_area_size(const VhostShadowVirtqueue *svq);
> >
> > +void vhost_svq_start(VhostShadowVirtqueue *svq, VirtIODevice *vdev,
> > +                     VirtQueue *vq);
> >   void vhost_svq_stop(VhostShadowVirtqueue *svq);
> >
> >   VhostShadowVirtqueue *vhost_svq_new(uint16_t qsize);
> > diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
> > b/hw/virtio/vhost-shadow-virtqueue.c
> > index 7c168075d7..a1a404f68f 100644
> > --- a/hw/virtio/vhost-shadow-virtqueue.c
> > +++ b/hw/virtio/vhost-shadow-virtqueue.c
> > @@ -9,6 +9,8 @@
> >
> >   #include "qemu/osdep.h"
> >   #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 "qemu/error-report.h"
> > @@ -36,6 +38,33 @@ typedef struct VhostShadowVirtqueue {
> >
> >       /* Guest's call notifier, where SVQ calls guest. */
> >       EventNotifier svq_call;
> > +
> > +    /* Virtio queue shadowing */
> > +    VirtQueue *vq;
> > +
> > +    /* Virtio device */
> > +    VirtIODevice *vdev;
> > +
> > +    /* Map for returning guest's descriptors */
> > +    VirtQueueElement **ring_id_maps;
> > +
> > +    /* Next VirtQueue element that guest made available */
> > +    VirtQueueElement *next_guest_avail_elem;
> > +
> > +    /* 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 last_used_idx;
> > +
> > +    /* Cache for the exposed notification flag */
> > +    bool notification;
> >   } VhostShadowVirtqueue;
> >
> >   #define INVALID_SVQ_KICK_FD -1
> > @@ -148,30 +177,294 @@ bool vhost_svq_ack_guest_features(uint64_t 
> > dev_features,
> >       return true;
> >   }
> >
> > -/* Forward guest notifications */
> > -static void vhost_handle_guest_kick(EventNotifier *n)
> > +/**
> > + * Number of descriptors that SVQ can make available from the guest.
> > + *
> > + * @svq   The svq
> > + */
> > +static uint16_t vhost_svq_available_slots(const VhostShadowVirtqueue *svq)
> >   {
> > -    VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue,
> > -                                             svq_kick);
> > +    return svq->vring.num - (svq->avail_idx_shadow - svq->shadow_used_idx);
> > +}
> > +
> > +static void vhost_svq_set_notification(VhostShadowVirtqueue *svq, bool 
> > enable)
> > +{
> > +    uint16_t notification_flag;
> >
> > -    if (unlikely(!event_notifier_test_and_clear(n))) {
> > +    if (svq->notification == enable) {
> > +        return;
> > +    }
> > +
> > +    notification_flag = cpu_to_le16(VRING_AVAIL_F_NO_INTERRUPT);
> > +
> > +    svq->notification = enable;
> > +    if (enable) {
> > +        svq->vring.avail->flags &= ~notification_flag;
> > +    } else {
> > +        svq->vring.avail->flags |= notification_flag;
> > +    }
> > +}
> > +
> > +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 ? cpu_to_le16(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 | cpu_to_le16(VRING_DESC_F_NEXT);
> > +        } else {
> > +            descs[i].flags = flags;
> > +        }
> > +        descs[i].addr = cpu_to_le64((hwaddr)iovec[n].iov_base);
> > +        descs[i].len = cpu_to_le32(iovec[n].iov_len);
> > +
> > +        last = i;
> > +        i = cpu_to_le16(descs[i].next);
> > +    }
> > +
> > +    svq->free_head = le16_to_cpu(descs[last].next);
> > +}
> > +
> > +static unsigned vhost_svq_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);
>
>
> Looks like this could be triggered by guest, we need fail instead assert
> here.
>

My understanding was that virtqueue_pop already sanitized that case,
but I'm not able to find where now. I will recheck and, in case it's
not, I will move to a failure.

>
> > +
> > +    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] = cpu_to_le16(head);
> > +    svq->avail_idx_shadow++;
> > +
> > +    /* Update avail index after the descriptor is wrote */
> > +    smp_wmb();
> > +    avail->idx = cpu_to_le16(svq->avail_idx_shadow);
> > +
> > +    return head;
> > +}
> > +
> > +static void vhost_svq_add(VhostShadowVirtqueue *svq, VirtQueueElement 
> > *elem)
> > +{
> > +    unsigned qemu_head = vhost_svq_add_split(svq, elem);
> > +
> > +    svq->ring_id_maps[qemu_head] = elem;
> > +}
> > +
> > +static void vhost_svq_kick(VhostShadowVirtqueue *svq)
> > +{
> > +    /* We need to expose available array entries before checking used 
> > flags */
> > +    smp_mb();
> > +    if (svq->vring.used->flags & VRING_USED_F_NO_NOTIFY) {
> >           return;
> >       }
> >
> >       event_notifier_set(&svq->hdev_kick);
> >   }
> >
> > -/* Forward vhost notifications */
> > +/**
> > + * Forward available buffers.
> > + *
> > + * @svq Shadow VirtQueue
> > + *
> > + * Note that this function does not guarantee that all guest's available
> > + * buffers are available to the device in SVQ avail ring. The guest may 
> > have
> > + * exposed a GPA / GIOVA congiuous buffer, but it may not be contiguous in 
> > qemu
> > + * vaddr.
> > + *
> > + * If that happens, guest's kick notifications will be disabled until 
> > device
> > + * makes some buffers used.
> > + */
> > +static void vhost_handle_guest_kick(VhostShadowVirtqueue *svq)
> > +{
> > +    /* Clear event notifier */
> > +    event_notifier_test_and_clear(&svq->svq_kick);
> > +
> > +    /* Make available as many buffers as possible */
> > +    do {
> > +        if (virtio_queue_get_notification(svq->vq)) {
> > +            virtio_queue_set_notification(svq->vq, false);
>
>
> This looks like an optimization the should belong to
> virtio_queue_set_notification() itself.
>

Sure we can move.

>
> > +        }
> > +
> > +        while (true) {
> > +            VirtQueueElement *elem;
> > +
> > +            if (svq->next_guest_avail_elem) {
> > +                elem = g_steal_pointer(&svq->next_guest_avail_elem);
> > +            } else {
> > +                elem = virtqueue_pop(svq->vq, sizeof(*elem));
> > +            }
> > +
> > +            if (!elem) {
> > +                break;
> > +            }
> > +
> > +            if (elem->out_num + elem->in_num >
> > +                vhost_svq_available_slots(svq)) {
> > +                /*
> > +                 * This condition is possible since a contiguous buffer in 
> > GPA
> > +                 * does not imply a contiguous buffer in qemu's VA
> > +                 * scatter-gather segments. If that happen, the buffer 
> > exposed
> > +                 * to the device needs to be a chain of descriptors at this
> > +                 * moment.
> > +                 *
> > +                 * SVQ cannot hold more available buffers if we are here:
> > +                 * queue the current guest descriptor and ignore further 
> > kicks
> > +                 * until some elements are used.
> > +                 */
> > +                svq->next_guest_avail_elem = elem;
> > +                return;
> > +            }
> > +
> > +            vhost_svq_add(svq, elem);
> > +            vhost_svq_kick(svq);
> > +        }
> > +
> > +        virtio_queue_set_notification(svq->vq, true);
> > +    } while (!virtio_queue_empty(svq->vq));
> > +}
> > +
> > +/**
> > + * Handle guest's kick.
> > + *
> > + * @n guest kick event notifier, the one that guest set to notify svq.
> > + */
> > +static void vhost_handle_guest_kick_notifier(EventNotifier *n)
> > +{
> > +    VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue,
> > +                                             svq_kick);
> > +    vhost_handle_guest_kick(svq);
> > +}
> > +
> > +static bool vhost_svq_more_used(VhostShadowVirtqueue *svq)
> > +{
> > +    if (svq->last_used_idx != svq->shadow_used_idx) {
> > +        return true;
> > +    }
> > +
> > +    svq->shadow_used_idx = cpu_to_le16(svq->vring.used->idx);
> > +
> > +    return svq->last_used_idx != svq->shadow_used_idx;
> > +}
> > +
> > +static VirtQueueElement *vhost_svq_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_svq_more_used(svq)) {
> > +        return NULL;
> > +    }
> > +
> > +    /* Only get used array entries after they have been exposed by dev */
> > +    smp_rmb();
> > +    last_used = svq->last_used_idx & (svq->vring.num - 1);
> > +    used_elem.id = le32_to_cpu(used->ring[last_used].id);
> > +    used_elem.len = le32_to_cpu(used->ring[last_used].len);
> > +
> > +    svq->last_used_idx++;
> > +    if (unlikely(used_elem.id >= svq->vring.num)) {
> > +        error_report("Device %s says index %u is used", svq->vdev->name,
> > +                     used_elem.id);
> > +        return NULL;
> > +    }
> > +
> > +    if (unlikely(!svq->ring_id_maps[used_elem.id])) {
> > +        error_report(
> > +            "Device %s says index %u is used, but it was not available",
> > +            svq->vdev->name, used_elem.id);
> > +        return NULL;
> > +    }
> > +
> > +    descs[used_elem.id].next = svq->free_head;
> > +    svq->free_head = used_elem.id;
> > +
> > +    svq->ring_id_maps[used_elem.id]->len = used_elem.len;
> > +    return g_steal_pointer(&svq->ring_id_maps[used_elem.id]);
> > +}
> > +
> > +static void vhost_svq_flush(VhostShadowVirtqueue *svq,
> > +                            bool check_for_avail_queue)
> > +{
> > +    VirtQueue *vq = svq->vq;
> > +
> > +    /* Make as many buffers as possible used. */
> > +    do {
> > +        unsigned i = 0;
> > +
> > +        vhost_svq_set_notification(svq, false);
> > +        while (true) {
> > +            g_autofree VirtQueueElement *elem = vhost_svq_get_buf(svq);
> > +            if (!elem) {
> > +                break;
> > +            }
> > +
> > +            if (unlikely(i >= svq->vring.num)) {
> > +                virtio_error(svq->vdev,
> > +                         "More than %u used buffers obtained in a %u size 
> > SVQ",
> > +                         i, svq->vring.num);
> > +                virtqueue_fill(vq, elem, elem->len, i);
> > +                virtqueue_flush(vq, i);
>
>
> Let's simply use virtqueue_push() here?
>

virtqueue_push support to fill and flush only one element, instead of
batch. I'm fine with either but I think the less updates to the used
idx, the better.

>
> > +                i = 0;
>
>
> Do we need to bail out here?
>

Yes I guess we can simply return.

>
> > +            }
> > +            virtqueue_fill(vq, elem, elem->len, i++);
> > +        }
> > +
> > +        virtqueue_flush(vq, i);
> > +        event_notifier_set(&svq->svq_call);
> > +
> > +        if (check_for_avail_queue && svq->next_guest_avail_elem) {
> > +            /*
> > +             * Avail ring was full when vhost_svq_flush was called, so 
> > it's a
> > +             * good moment to make more descriptors available if possible
> > +             */
> > +            vhost_handle_guest_kick(svq);
>
>
> Is there better to have a similar check as vhost_handle_guest_kick() did?
>
>              if (elem->out_num + elem->in_num >
>                  vhost_svq_available_slots(svq)) {
>

It will be duplicated when we call vhost_handle_guest_kick, won't it?

>
> > +        }
> > +
> > +        vhost_svq_set_notification(svq, true);
>
>
> A mb() is needed here? Otherwise we may lost a call here (where
> vhost_svq_more_used() is run before vhost_svq_set_notification()).
>

I'm confused here then, I thought you said this is just a hint so
there was no need? [1]. I think the memory barrier is needed too.

>
> > +    } while (vhost_svq_more_used(svq));
> > +}
> > +
> > +/**
> > + * Forward used buffers.
> > + *
> > + * @n hdev call event notifier, the one that device set to notify svq.
> > + *
> > + * Note that we are not making any buffers available in the loop, there is 
> > no
> > + * way that it runs more than virtqueue size times.
> > + */
> >   static void vhost_svq_handle_call(EventNotifier *n)
> >   {
> >       VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue,
> >                                                hdev_call);
> >
> > -    if (unlikely(!event_notifier_test_and_clear(n))) {
> > -        return;
> > -    }
> > +    /* Clear event notifier */
> > +    event_notifier_test_and_clear(n);
>
>
> Any reason that we remove the above check?
>

This comes from the previous versions, where this made sure we missed
no used buffers in the process of switching to SVQ mode.

If we enable SVQ from the beginning I think we can rely on getting all
the device's used buffer notifications, so let me think a little bit
and I can move to check the eventfd.

>
> >
> > -    event_notifier_set(&svq->svq_call);
> > +    vhost_svq_flush(svq, true);
> >   }
> >
> >   /**
> > @@ -258,13 +551,38 @@ void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue 
> > *svq, int svq_kick_fd)
> >        * need to explicitely check for them.
> >        */
> >       event_notifier_init_fd(&svq->svq_kick, svq_kick_fd);
> > -    event_notifier_set_handler(&svq->svq_kick, vhost_handle_guest_kick);
> > +    event_notifier_set_handler(&svq->svq_kick,
> > +                               vhost_handle_guest_kick_notifier);
> >
> >       if (!check_old || event_notifier_test_and_clear(&tmp)) {
> >           event_notifier_set(&svq->hdev_kick);
> >       }
> >   }
> >
> > +/**
> > + * Start shadow virtqueue operation.
> > + *
> > + * @svq Shadow Virtqueue
> > + * @vdev        VirtIO device
> > + * @vq          Virtqueue to shadow
> > + */
> > +void vhost_svq_start(VhostShadowVirtqueue *svq, VirtIODevice *vdev,
> > +                     VirtQueue *vq)
> > +{
> > +    svq->next_guest_avail_elem = NULL;
> > +    svq->avail_idx_shadow = 0;
> > +    svq->shadow_used_idx = 0;
> > +    svq->last_used_idx = 0;
> > +    svq->vdev = vdev;
> > +    svq->vq = vq;
> > +
> > +    memset(svq->vring.avail, 0, sizeof(*svq->vring.avail));
> > +    memset(svq->vring.used, 0, sizeof(*svq->vring.avail));
> > +    for (unsigned i = 0; i < svq->vring.num - 1; i++) {
> > +        svq->vring.desc[i].next = cpu_to_le16(i + 1);
> > +    }
> > +}
> > +
> >   /**
> >    * Stop shadow virtqueue operation.
> >    * @svq Shadow Virtqueue
> > @@ -272,6 +590,28 @@ void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue 
> > *svq, int svq_kick_fd)
> >   void vhost_svq_stop(VhostShadowVirtqueue *svq)
> >   {
> >       event_notifier_set_handler(&svq->svq_kick, NULL);
> > +    g_autofree VirtQueueElement *next_avail_elem = NULL;
> > +
> > +    if (!svq->vq) {
> > +        return;
> > +    }
> > +
> > +    /* Send all pending used descriptors to guest */
> > +    vhost_svq_flush(svq, false);
> > +
> > +    for (unsigned i = 0; i < svq->vring.num; ++i) {
> > +        g_autofree VirtQueueElement *elem = NULL;
> > +        elem = g_steal_pointer(&svq->ring_id_maps[i]);
> > +        if (elem) {
> > +            virtqueue_detach_element(svq->vq, elem, elem->len);
> > +        }
> > +    }
> > +
> > +    next_avail_elem = g_steal_pointer(&svq->next_guest_avail_elem);
> > +    if (next_avail_elem) {
> > +        virtqueue_detach_element(svq->vq, next_avail_elem,
> > +                                 next_avail_elem->len);
> > +    }
> >   }
> >
> >   /**
> > @@ -316,7 +656,7 @@ VhostShadowVirtqueue *vhost_svq_new(uint16_t qsize)
> >       memset(svq->vring.desc, 0, driver_size);
> >       svq->vring.used = qemu_memalign(qemu_real_host_page_size, 
> > device_size);
> >       memset(svq->vring.used, 0, device_size);
> > -
> > +    svq->ring_id_maps = g_new0(VirtQueueElement *, qsize);
> >       event_notifier_set_handler(&svq->hdev_call, vhost_svq_handle_call);
> >       return g_steal_pointer(&svq);
> >
> > @@ -335,6 +675,7 @@ void vhost_svq_free(VhostShadowVirtqueue *vq)
> >       event_notifier_cleanup(&vq->hdev_kick);
> >       event_notifier_set_handler(&vq->hdev_call, NULL);
> >       event_notifier_cleanup(&vq->hdev_call);
> > +    g_free(vq->ring_id_maps);
> >       qemu_vfree(vq->vring.desc);
> >       qemu_vfree(vq->vring.used);
> >       g_free(vq);
> > diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> > index 53e14bafa0..0e5c00ed7e 100644
> > --- a/hw/virtio/vhost-vdpa.c
> > +++ b/hw/virtio/vhost-vdpa.c
> > @@ -752,9 +752,9 @@ static int vhost_vdpa_set_vring_call(struct vhost_dev 
> > *dev,
> >    * Note that this function does not rewind kick file descriptor if cannot 
> > set
> >    * call one.
> >    */
> > -static bool vhost_vdpa_svq_setup(struct vhost_dev *dev,
> > -                                VhostShadowVirtqueue *svq,
> > -                                unsigned idx)
> > +static int vhost_vdpa_svq_set_fds(struct vhost_dev *dev,
> > +                                  VhostShadowVirtqueue *svq,
> > +                                  unsigned idx)
> >   {
> >       struct vhost_vring_file file = {
> >           .index = dev->vq_index + idx,
> > @@ -767,7 +767,7 @@ static bool vhost_vdpa_svq_setup(struct vhost_dev *dev,
> >       r = vhost_vdpa_set_vring_dev_kick(dev, &file);
> >       if (unlikely(r != 0)) {
> >           error_report("Can't set device kick fd (%d)", -r);
> > -        return false;
> > +        return r;
> >       }
> >
> >       event_notifier = vhost_svq_get_svq_call_notifier(svq);
> > @@ -777,6 +777,99 @@ static bool vhost_vdpa_svq_setup(struct vhost_dev *dev,
> >           error_report("Can't set device call fd (%d)", -r);
> >       }
> >
> > +    return r;
> > +}
> > +
> > +/**
> > + * Unmap SVQ area in the device
> > + */
> > +static bool vhost_vdpa_svq_unmap_ring(struct vhost_vdpa *v, hwaddr iova,
> > +                                      hwaddr size)
> > +{
> > +    int r;
> > +
> > +    size = ROUND_UP(size, qemu_real_host_page_size);
> > +    r = vhost_vdpa_dma_unmap(v, iova, size);
> > +    return r == 0;
> > +}
> > +
> > +static bool vhost_vdpa_svq_unmap_rings(struct vhost_dev *dev,
> > +                                       const VhostShadowVirtqueue *svq)
> > +{
> > +    struct vhost_vdpa *v = dev->opaque;
> > +    struct vhost_vring_addr svq_addr;
> > +    size_t device_size = vhost_svq_device_area_size(svq);
> > +    size_t driver_size = vhost_svq_driver_area_size(svq);
> > +    bool ok;
> > +
> > +    vhost_svq_get_vring_addr(svq, &svq_addr);
> > +
> > +    ok = vhost_vdpa_svq_unmap_ring(v, svq_addr.desc_user_addr, 
> > driver_size);
> > +    if (unlikely(!ok)) {
> > +        return false;
> > +    }
> > +
> > +    return vhost_vdpa_svq_unmap_ring(v, svq_addr.used_user_addr, 
> > device_size);
> > +}
> > +
> > +/**
> > + * Map shadow virtqueue rings in device
> > + *
> > + * @dev   The vhost device
> > + * @svq   The shadow virtqueue
> > + */
> > +static bool vhost_vdpa_svq_map_rings(struct vhost_dev *dev,
> > +                                     const VhostShadowVirtqueue *svq)
> > +{
> > +    struct vhost_vdpa *v = dev->opaque;
> > +    struct vhost_vring_addr svq_addr;
> > +    size_t device_size = vhost_svq_device_area_size(svq);
> > +    size_t driver_size = vhost_svq_driver_area_size(svq);
> > +    int r;
> > +
> > +    vhost_svq_get_vring_addr(svq, &svq_addr);
> > +
> > +    r = vhost_vdpa_dma_map(v, svq_addr.desc_user_addr, driver_size,
> > +                           (void *)svq_addr.desc_user_addr, true);
> > +    if (unlikely(r != 0)) {
> > +        return false;
> > +    }
> > +
> > +    r = vhost_vdpa_dma_map(v, svq_addr.used_user_addr, device_size,
> > +                           (void *)svq_addr.used_user_addr, false);
>
>
> Do we need unmap the driver area if we fail here?
>

Yes, this used to trust in unmap them at the disabling of SVQ. Now I
think we need to unmap as you say.

Thanks!

[1] 
https://lists.linuxfoundation.org/pipermail/virtualization/2021-March/053322.html

> Thanks
>
>
> > +    return r == 0;
> > +}
> > +
> > +static bool vhost_vdpa_svq_setup(struct vhost_dev *dev,
> > +                                VhostShadowVirtqueue *svq,
> > +                                unsigned idx)
> > +{
> > +    uint16_t vq_index = dev->vq_index + idx;
> > +    struct vhost_vring_state s = {
> > +        .index = vq_index,
> > +    };
> > +    int r;
> > +    bool ok;
> > +
> > +    r = vhost_vdpa_set_dev_vring_base(dev, &s);
> > +    if (unlikely(r)) {
> > +        error_report("Can't set vring base (%d)", r);
> > +        return false;
> > +    }
> > +
> > +    s.num = vhost_svq_get_num(svq);
> > +    r = vhost_vdpa_set_dev_vring_num(dev, &s);
> > +    if (unlikely(r)) {
> > +        error_report("Can't set vring num (%d)", r);
> > +        return false;
> > +    }
> > +
> > +    ok = vhost_vdpa_svq_map_rings(dev, svq);
> > +    if (unlikely(!ok)) {
> > +        return false;
> > +    }
> > +
> > +    r = vhost_vdpa_svq_set_fds(dev, svq, idx);
> >       return r == 0;
> >   }
> >
> > @@ -788,14 +881,24 @@ static int vhost_vdpa_dev_start(struct vhost_dev 
> > *dev, bool started)
> >       if (started) {
> >           vhost_vdpa_host_notifiers_init(dev);
> >           for (unsigned i = 0; i < v->shadow_vqs->len; ++i) {
> > +            VirtQueue *vq = virtio_get_queue(dev->vdev, dev->vq_index + i);
> >               VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, 
> > i);
> >               bool ok = vhost_vdpa_svq_setup(dev, svq, i);
> >               if (unlikely(!ok)) {
> >                   return -1;
> >               }
> > +            vhost_svq_start(svq, dev->vdev, vq);
> >           }
> >           vhost_vdpa_set_vring_ready(dev);
> >       } else {
> > +        for (unsigned i = 0; i < v->shadow_vqs->len; ++i) {
> > +            VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs,
> > +                                                          i);
> > +            bool ok = vhost_vdpa_svq_unmap_rings(dev, svq);
> > +            if (unlikely(!ok)) {
> > +                return -1;
> > +            }
> > +        }
> >           vhost_vdpa_host_notifiers_uninit(dev, dev->nvqs);
> >       }
> >
>