Re: [PATCH v2 02/14] vhost: Add Shadow VirtQueue kick forwarding capabilities

[Eugenio Perez Martin]

On Mon, Feb 28, 2022 at 3:57 AM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 在 2022/2/27 下午9:40, Eugenio Pérez 写道:
> > At this mode no buffer forwarding will be performed in SVQ mode: Qemu
> > will just forward the guest's kicks to the device.
> >
> > Host memory notifiers regions are left out for simplicity, and they will
> > not be addressed in this series.
> >
> > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > ---
> >   hw/virtio/vhost-shadow-virtqueue.h |  14 +++
> >   include/hw/virtio/vhost-vdpa.h     |   4 +
> >   hw/virtio/vhost-shadow-virtqueue.c |  52 +++++++++++
> >   hw/virtio/vhost-vdpa.c             | 145 ++++++++++++++++++++++++++++-
> >   4 files changed, 213 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/virtio/vhost-shadow-virtqueue.h 
> > b/hw/virtio/vhost-shadow-virtqueue.h
> > index f1519e3c7b..1cbc87d5d8 100644
> > --- a/hw/virtio/vhost-shadow-virtqueue.h
> > +++ b/hw/virtio/vhost-shadow-virtqueue.h
> > @@ -18,8 +18,22 @@ typedef struct VhostShadowVirtqueue {
> >       EventNotifier hdev_kick;
> >       /* Shadow call notifier, sent to vhost */
> >       EventNotifier hdev_call;
> > +
> > +    /*
> > +     * Borrowed virtqueue's guest to host notifier. To borrow it in this 
> > event
> > +     * notifier allows to recover the VhostShadowVirtqueue from the event 
> > loop
> > +     * easily. If we use the VirtQueue's one, we don't have an easy way to
> > +     * retrieve VhostShadowVirtqueue.
> > +     *
> > +     * So shadow virtqueue must not clean it, or we would lose VirtQueue 
> > one.
> > +     */
> > +    EventNotifier svq_kick;
> >   } VhostShadowVirtqueue;
> >
> > +void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd);
> > +
> > +void vhost_svq_stop(VhostShadowVirtqueue *svq);
> > +
> >   VhostShadowVirtqueue *vhost_svq_new(void);
> >
> >   void vhost_svq_free(gpointer vq);
> > diff --git a/include/hw/virtio/vhost-vdpa.h b/include/hw/virtio/vhost-vdpa.h
> > index 3ce79a646d..009a9f3b6b 100644
> > --- a/include/hw/virtio/vhost-vdpa.h
> > +++ b/include/hw/virtio/vhost-vdpa.h
> > @@ -12,6 +12,8 @@
> >   #ifndef HW_VIRTIO_VHOST_VDPA_H
> >   #define HW_VIRTIO_VHOST_VDPA_H
> >
> > +#include <gmodule.h>
> > +
> >   #include "hw/virtio/virtio.h"
> >   #include "standard-headers/linux/vhost_types.h"
> >
> > @@ -27,6 +29,8 @@ typedef struct vhost_vdpa {
> >       bool iotlb_batch_begin_sent;
> >       MemoryListener listener;
> >       struct vhost_vdpa_iova_range iova_range;
> > +    bool shadow_vqs_enabled;
> > +    GPtrArray *shadow_vqs;
> >       struct vhost_dev *dev;
> >       VhostVDPAHostNotifier notifier[VIRTIO_QUEUE_MAX];
> >   } VhostVDPA;
> > diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
> > b/hw/virtio/vhost-shadow-virtqueue.c
> > index 019cf1950f..a5d0659f86 100644
> > --- a/hw/virtio/vhost-shadow-virtqueue.c
> > +++ b/hw/virtio/vhost-shadow-virtqueue.c
> > @@ -11,6 +11,56 @@
> >   #include "hw/virtio/vhost-shadow-virtqueue.h"
> >
> >   #include "qemu/error-report.h"
> > +#include "qemu/main-loop.h"
> > +#include "linux-headers/linux/vhost.h"
> > +
> > +/** Forward guest notifications */
> > +static void vhost_handle_guest_kick(EventNotifier *n)
> > +{
> > +    VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue,
> > +                                             svq_kick);
> > +    event_notifier_test_and_clear(n);
> > +    event_notifier_set(&svq->hdev_kick);
> > +}
> > +
> > +/**
> > + * Set a new file descriptor for the guest to kick the SVQ and notify for 
> > avail
> > + *
> > + * @svq          The svq
> > + * @svq_kick_fd  The svq kick fd
> > + *
> > + * Note that the SVQ will never close the old file descriptor.
> > + */
> > +void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd)
> > +{
> > +    EventNotifier *svq_kick = &svq->svq_kick;
> > +    bool poll_stop = VHOST_FILE_UNBIND != event_notifier_get_fd(svq_kick);
>
>
> I wonder if this is robust. E.g is there any chance that may end up with
> both poll_stop and poll_start are false?
>

I cannot make that happen in qemu, but the function supports that case
well: It will do nothing. It's more or less the same code as used in
the vhost kernel, and is the expected behaviour if you send two
VHOST_FILE_UNBIND one right after another to me.

> If not, can we simple detect poll_stop as below and treat !poll_start
> and poll_stop?
>

I'm not sure what does it add. Is there an unexpected consequence with
the current do-nothing behavior I've missed?

Thanks!

> Other looks good.
>
> Thanks
>
>
> > +    bool poll_start = svq_kick_fd != VHOST_FILE_UNBIND;
> > +
> > +    if (poll_stop) {
> > +        event_notifier_set_handler(svq_kick, NULL);
> > +    }
> > +
> > +    /*
> > +     * event_notifier_set_handler already checks for guest's notifications 
> > if
> > +     * they arrive at the new file descriptor in the switch, so there is no
> > +     * need to explicitly check for them.
> > +     */
> > +    if (poll_start) {
> > +        event_notifier_init_fd(svq_kick, svq_kick_fd);
> > +        event_notifier_set(svq_kick);
> > +        event_notifier_set_handler(svq_kick, vhost_handle_guest_kick);
> > +    }
> > +}
> > +
> > +/**
> > + * Stop the shadow virtqueue operation.
> > + * @svq Shadow Virtqueue
> > + */
> > +void vhost_svq_stop(VhostShadowVirtqueue *svq)
> > +{
> > +    event_notifier_set_handler(&svq->svq_kick, NULL);
> > +}
> >
> >   /**
> >    * Creates vhost shadow virtqueue, and instructs the vhost device to use 
> > the
> > @@ -39,6 +89,7 @@ VhostShadowVirtqueue *vhost_svq_new(void)
> >           goto err_init_hdev_call;
> >       }
> >
> > +    event_notifier_init_fd(&svq->svq_kick, VHOST_FILE_UNBIND);
> >       return g_steal_pointer(&svq);
> >
> >   err_init_hdev_call:
> > @@ -56,6 +107,7 @@ err_init_hdev_kick:
> >   void vhost_svq_free(gpointer pvq)
> >   {
> >       VhostShadowVirtqueue *vq = pvq;
> > +    vhost_svq_stop(vq);
> >       event_notifier_cleanup(&vq->hdev_kick);
> >       event_notifier_cleanup(&vq->hdev_call);
> >       g_free(vq);
> > diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> > index 04ea43704f..454bf50735 100644
> > --- a/hw/virtio/vhost-vdpa.c
> > +++ b/hw/virtio/vhost-vdpa.c
> > @@ -17,12 +17,14 @@
> >   #include "hw/virtio/vhost.h"
> >   #include "hw/virtio/vhost-backend.h"
> >   #include "hw/virtio/virtio-net.h"
> > +#include "hw/virtio/vhost-shadow-virtqueue.h"
> >   #include "hw/virtio/vhost-vdpa.h"
> >   #include "exec/address-spaces.h"
> >   #include "qemu/main-loop.h"
> >   #include "cpu.h"
> >   #include "trace.h"
> >   #include "qemu-common.h"
> > +#include "qapi/error.h"
> >
> >   /*
> >    * Return one past the end of the end of section. Be careful with uint64_t
> > @@ -342,6 +344,30 @@ static bool vhost_vdpa_one_time_request(struct 
> > vhost_dev *dev)
> >       return v->index != 0;
> >   }
> >
> > +static int vhost_vdpa_init_svq(struct vhost_dev *hdev, struct vhost_vdpa 
> > *v,
> > +                               Error **errp)
> > +{
> > +    g_autoptr(GPtrArray) shadow_vqs = NULL;
> > +
> > +    if (!v->shadow_vqs_enabled) {
> > +        return 0;
> > +    }
> > +
> > +    shadow_vqs = g_ptr_array_new_full(hdev->nvqs, vhost_svq_free);
> > +    for (unsigned n = 0; n < hdev->nvqs; ++n) {
> > +        g_autoptr(VhostShadowVirtqueue) svq = vhost_svq_new();
> > +
> > +        if (unlikely(!svq)) {
> > +            error_setg(errp, "Cannot create svq %u", n);
> > +            return -1;
> > +        }
> > +        g_ptr_array_add(shadow_vqs, g_steal_pointer(&svq));
> > +    }
> > +
> > +    v->shadow_vqs = g_steal_pointer(&shadow_vqs);
> > +    return 0;
> > +}
> > +
> >   static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque, Error 
> > **errp)
> >   {
> >       struct vhost_vdpa *v;
> > @@ -364,6 +390,10 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void 
> > *opaque, Error **errp)
> >       dev->opaque =  opaque ;
> >       v->listener = vhost_vdpa_memory_listener;
> >       v->msg_type = VHOST_IOTLB_MSG_V2;
> > +    ret = vhost_vdpa_init_svq(dev, v, errp);
> > +    if (ret) {
> > +        goto err;
> > +    }
> >
> >       vhost_vdpa_get_iova_range(v);
> >
> > @@ -375,6 +405,10 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void 
> > *opaque, Error **errp)
> >                                  VIRTIO_CONFIG_S_DRIVER);
> >
> >       return 0;
> > +
> > +err:
> > +    ram_block_discard_disable(false);
> > +    return ret;
> >   }
> >
> >   static void vhost_vdpa_host_notifier_uninit(struct vhost_dev *dev,
> > @@ -444,8 +478,14 @@ err:
> >
> >   static void vhost_vdpa_host_notifiers_init(struct vhost_dev *dev)
> >   {
> > +    struct vhost_vdpa *v = dev->opaque;
> >       int i;
> >
> > +    if (v->shadow_vqs_enabled) {
> > +        /* FIXME SVQ is not compatible with host notifiers mr */
> > +        return;
> > +    }
> > +
> >       for (i = dev->vq_index; i < dev->vq_index + dev->nvqs; i++) {
> >           if (vhost_vdpa_host_notifier_init(dev, i)) {
> >               goto err;
> > @@ -459,6 +499,21 @@ err:
> >       return;
> >   }
> >
> > +static void vhost_vdpa_svq_cleanup(struct vhost_dev *dev)
> > +{
> > +    struct vhost_vdpa *v = dev->opaque;
> > +    size_t idx;
> > +
> > +    if (!v->shadow_vqs) {
> > +        return;
> > +    }
> > +
> > +    for (idx = 0; idx < v->shadow_vqs->len; ++idx) {
> > +        vhost_svq_stop(g_ptr_array_index(v->shadow_vqs, idx));
> > +    }
> > +    g_ptr_array_free(v->shadow_vqs, true);
> > +}
> > +
> >   static int vhost_vdpa_cleanup(struct vhost_dev *dev)
> >   {
> >       struct vhost_vdpa *v;
> > @@ -467,6 +522,7 @@ static int vhost_vdpa_cleanup(struct vhost_dev *dev)
> >       trace_vhost_vdpa_cleanup(dev, v);
> >       vhost_vdpa_host_notifiers_uninit(dev, dev->nvqs);
> >       memory_listener_unregister(&v->listener);
> > +    vhost_vdpa_svq_cleanup(dev);
> >
> >       dev->opaque = NULL;
> >       ram_block_discard_disable(false);
> > @@ -558,11 +614,26 @@ static int vhost_vdpa_get_device_id(struct vhost_dev 
> > *dev,
> >       return ret;
> >   }
> >
> > +static void vhost_vdpa_reset_svq(struct vhost_vdpa *v)
> > +{
> > +    if (!v->shadow_vqs_enabled) {
> > +        return;
> > +    }
> > +
> > +    for (unsigned i = 0; i < v->shadow_vqs->len; ++i) {
> > +        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, i);
> > +        vhost_svq_stop(svq);
> > +    }
> > +}
> > +
> >   static int vhost_vdpa_reset_device(struct vhost_dev *dev)
> >   {
> > +    struct vhost_vdpa *v = dev->opaque;
> >       int ret;
> >       uint8_t status = 0;
> >
> > +    vhost_vdpa_reset_svq(v);
> > +
> >       ret = vhost_vdpa_call(dev, VHOST_VDPA_SET_STATUS, &status);
> >       trace_vhost_vdpa_reset_device(dev, status);
> >       return ret;
> > @@ -646,13 +717,75 @@ static int vhost_vdpa_get_config(struct vhost_dev 
> > *dev, uint8_t *config,
> >       return ret;
> >    }
> >
> > +static int vhost_vdpa_set_vring_dev_kick(struct vhost_dev *dev,
> > +                                         struct vhost_vring_file *file)
> > +{
> > +    trace_vhost_vdpa_set_vring_kick(dev, file->index, file->fd);
> > +    return vhost_vdpa_call(dev, VHOST_SET_VRING_KICK, file);
> > +}
> > +
> > +/**
> > + * Set the shadow virtqueue descriptors to the device
> > + *
> > + * @dev   The vhost device model
> > + * @svq   The shadow virtqueue
> > + * @idx   The index of the virtqueue in the vhost device
> > + * @errp  Error
> > + */
> > +static bool vhost_vdpa_svq_setup(struct vhost_dev *dev,
> > +                                 VhostShadowVirtqueue *svq,
> > +                                 unsigned idx,
> > +                                 Error **errp)
> > +{
> > +    struct vhost_vring_file file = {
> > +        .index = dev->vq_index + idx,
> > +    };
> > +    const EventNotifier *event_notifier = &svq->hdev_kick;
> > +    int r;
> > +
> > +    file.fd = event_notifier_get_fd(event_notifier);
> > +    r = vhost_vdpa_set_vring_dev_kick(dev, &file);
> > +    if (unlikely(r != 0)) {
> > +        error_setg_errno(errp, -r, "Can't set device kick fd");
> > +    }
> > +
> > +    return r == 0;
> > +}
> > +
> > +static bool vhost_vdpa_svqs_start(struct vhost_dev *dev)
> > +{
> > +    struct vhost_vdpa *v = dev->opaque;
> > +    Error *err = NULL;
> > +    unsigned i;
> > +
> > +    if (!v->shadow_vqs) {
> > +        return true;
> > +    }
> > +
> > +    for (i = 0; i < v->shadow_vqs->len; ++i) {
> > +        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, i);
> > +        bool ok = vhost_vdpa_svq_setup(dev, svq, i, &err);
> > +        if (unlikely(!ok)) {
> > +            error_reportf_err(err, "Cannot setup SVQ %u: ", i);
> > +            return false;
> > +        }
> > +    }
> > +
> > +    return true;
> > +}
> > +
> >   static int vhost_vdpa_dev_start(struct vhost_dev *dev, bool started)
> >   {
> >       struct vhost_vdpa *v = dev->opaque;
> > +    bool ok;
> >       trace_vhost_vdpa_dev_start(dev, started);
> >
> >       if (started) {
> >           vhost_vdpa_host_notifiers_init(dev);
> > +        ok = vhost_vdpa_svqs_start(dev);
> > +        if (unlikely(!ok)) {
> > +            return -1;
> > +        }
> >           vhost_vdpa_set_vring_ready(dev);
> >       } else {
> >           vhost_vdpa_host_notifiers_uninit(dev, dev->nvqs);
> > @@ -724,8 +857,16 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev 
> > *dev,
> >   static int vhost_vdpa_set_vring_kick(struct vhost_dev *dev,
> >                                          struct vhost_vring_file *file)
> >   {
> > -    trace_vhost_vdpa_set_vring_kick(dev, file->index, file->fd);
> > -    return vhost_vdpa_call(dev, VHOST_SET_VRING_KICK, file);
> > +    struct vhost_vdpa *v = dev->opaque;
> > +    int vdpa_idx = file->index - dev->vq_index;
> > +
> > +    if (v->shadow_vqs_enabled) {
> > +        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, 
> > vdpa_idx);
> > +        vhost_svq_set_svq_kick_fd(svq, file->fd);
> > +        return 0;
> > +    } else {
> > +        return vhost_vdpa_set_vring_dev_kick(dev, file);
> > +    }
> >   }
> >
> >   static int vhost_vdpa_set_vring_call(struct vhost_dev *dev,
>