Re: [PATCH 06/31] vhost: Route guest->host notification through shadow virtqueue

[Jason Wang <jasowang@redhat.com>]

在 2022/1/31 下午7:33, Eugenio Perez Martin 写道:
> On Fri, Jan 28, 2022 at 7:57 AM Jason Wang <jasowang@redhat.com> wrote:
>>
>> 在 2022/1/22 上午4:27, Eugenio Pérez 写道:
>>> At this moment no buffer forwarding will be performed in SVQ mode: Qemu
>>> just forward the guest's kicks to the device. This commit also set up
>>> SVQs in the vhost device.
>>>
>>> Host memory notifiers regions are left out for simplicity, and they will
>>> not be addressed in this series.
>>
>> I wonder if it's better to squash this into patch 5 since it gives us a
>> full guest->host forwarding.
>>
> I'm fine with that if you think it makes the review easier.


Yes please.


>
>>> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
>>> ---
>>>    include/hw/virtio/vhost-vdpa.h |   4 ++
>>>    hw/virtio/vhost-vdpa.c         | 122 ++++++++++++++++++++++++++++++++-
>>>    2 files changed, 124 insertions(+), 2 deletions(-)
>>>
>>> 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-vdpa.c b/hw/virtio/vhost-vdpa.c
>>> index 6c10a7f05f..18de14f0fb 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
>>> @@ -409,8 +411,14 @@ 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) {
>>> +        /* SVQ is not compatible with host notifiers mr */
>>
>> I guess there should be a TODO or FIXME here.
>>
> Sure I can add it.
>
>>> +        return;
>>> +    }
>>> +
>>>        for (i = dev->vq_index; i < dev->vq_index + dev->nvqs; i++) {
>>>            if (vhost_vdpa_host_notifier_init(dev, i)) {
>>>                goto err;
>>> @@ -424,6 +432,17 @@ err:
>>>        return;
>>>    }
>>>
>>> +static void vhost_vdpa_svq_cleanup(struct vhost_dev *dev)
>>> +{
>>> +    struct vhost_vdpa *v = dev->opaque;
>>> +    size_t idx;
>>> +
>>> +    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;
>>> @@ -432,6 +451,7 @@ 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);
>>> @@ -507,9 +527,15 @@ static int vhost_vdpa_get_device_id(struct vhost_dev *dev,
>>>
>>>    static int vhost_vdpa_reset_device(struct vhost_dev *dev)
>>>    {
>>> +    struct vhost_vdpa *v = dev->opaque;
>>>        int ret;
>>>        uint8_t status = 0;
>>>
>>> +    for (unsigned i = 0; i < v->shadow_vqs->len; ++i) {
>>> +        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, i);
>>> +        vhost_svq_stop(svq);
>>> +    }
>>> +
>>>        ret = vhost_vdpa_call(dev, VHOST_VDPA_SET_STATUS, &status);
>>>        trace_vhost_vdpa_reset_device(dev, status);
>>>        return ret;
>>> @@ -639,13 +665,28 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev *dev,
>>>        return ret;
>>>    }
>>>
>>> -static int vhost_vdpa_set_vring_kick(struct vhost_dev *dev,
>>> -                                       struct vhost_vring_file *file)
>>> +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);
>>>    }
>>>
>>> +static int vhost_vdpa_set_vring_kick(struct vhost_dev *dev,
>>> +                                       struct vhost_vring_file *file)
>>> +{
>>> +    struct vhost_vdpa *v = dev->opaque;
>>> +    int vdpa_idx = vhost_vdpa_get_vq_index(dev, file->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,
>>>                                           struct vhost_vring_file *file)
>>>    {
>>> @@ -653,6 +694,33 @@ static int vhost_vdpa_set_vring_call(struct vhost_dev *dev,
>>>        return vhost_vdpa_call(dev, VHOST_SET_VRING_CALL, file);
>>>    }
>>>
>>> +/**
>>> + * Set 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
>>> + */
>>> +static bool vhost_vdpa_svq_setup(struct vhost_dev *dev,
>>> +                                VhostShadowVirtqueue *svq,
>>> +                                unsigned idx)
>>> +{
>>> +    struct vhost_vring_file file = {
>>> +        .index = dev->vq_index + idx,
>>> +    };
>>> +    const EventNotifier *event_notifier;
>>> +    int r;
>>> +
>>> +    event_notifier = vhost_svq_get_dev_kick_notifier(svq);
>>
>> A question, any reason for making VhostShadowVirtqueue private? If we
>> export it in .h we don't need helper to access its member like
>> vhost_svq_get_dev_kick_notifier().
>>
> To export it it's always a possibility of course, but that direct
> access will not be thread safe if we decide to move SVQ to its own
> iothread for example.


I don't get this, maybe you can give me an example.


>
> I feel it will be easier to work with it this way but it might be that
> I'm just used to making as much as possible private. Not like it's
> needed to use the helpers in the hot paths, only in the setup and
> teardown.
>
>> Note that vhost_dev is a public structure.
>>
> Sure we could embed in vhost_virtqueue if we choose to do it that way,
> for example.
>
>>> +    file.fd = event_notifier_get_fd(event_notifier);
>>> +    r = vhost_vdpa_set_vring_dev_kick(dev, &file);
>>> +    if (unlikely(r != 0)) {
>>> +        error_report("Can't set device kick fd (%d)", -r);
>>> +    }
>>
>> I wonder whether or not we can generalize the logic here and
>> vhost_vdpa_set_vring_kick(). There's nothing vdpa specific unless the
>> vhost_ops->set_vring_kick().
>>
> If we call vhost_ops->set_vring_kick we are setting guest->SVQ kick
> notifier, not SVQ -> vDPA device, because the
> if(v->shadow_vqs_enabled). All of the modified ops callbacks are
> hiding the actual device from the vhost subsystem so we need to
> explicitly use the newly created _dev_ ones.


Ok, I'm fine to start with vhost_vdpa specific code.


>
>>> +
>>> +    return r == 0;
>>> +}
>>> +
>>>    static int vhost_vdpa_dev_start(struct vhost_dev *dev, bool started)
>>>    {
>>>        struct vhost_vdpa *v = dev->opaque;
>>> @@ -660,6 +728,13 @@ 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) {
>>> +            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_vdpa_set_vring_ready(dev);
>>>        } else {
>>>            vhost_vdpa_host_notifiers_uninit(dev, dev->nvqs);
>>> @@ -737,6 +812,41 @@ static bool  vhost_vdpa_force_iommu(struct vhost_dev *dev)
>>>        return true;
>>>    }
>>>
>>> +/**
>>> + * Adaptor function to free shadow virtqueue through gpointer
>>> + *
>>> + * @svq   The Shadow Virtqueue
>>> + */
>>> +static void vhost_psvq_free(gpointer svq)
>>> +{
>>> +    vhost_svq_free(svq);
>>> +}
>>
>> Any reason for such indirection? Can we simply use vhost_svq_free()?
>>
> GCC complains about different types. I think we could do a function
> type cast and it's valid for every architecture qemu supports, but the
> indirection seems cleaner to me, and I would be surprised if the
> compiler does not optimize it away in the cases that the casting are
> valid.
>
> ../hw/virtio/vhost-vdpa.c:1186:60: error: incompatible function
> pointer types passing 'void (VhostShadowVirtqueue *)' (aka 'void
> (struct VhostShadowVirtqueue *)') to parameter of type
> 'GDestroyNotify' (aka 'void (*)(void *)')


Or just change vhost_svq_free() to take gpointer instead? Then we don't 
need a cast.

Thanks

>
> Thanks!
>
>> Thanks
>>
>>
>>> +
>>> +static int vhost_vdpa_init_svq(struct vhost_dev *hdev, struct vhost_vdpa *v,
>>> +                               Error **errp)
>>> +{
>>> +    size_t n_svqs = v->shadow_vqs_enabled ? hdev->nvqs : 0;
>>> +    g_autoptr(GPtrArray) shadow_vqs = g_ptr_array_new_full(n_svqs,
>>> +                                                           vhost_psvq_free);
>>> +    if (!v->shadow_vqs_enabled) {
>>> +        goto out;
>>> +    }
>>> +
>>> +    for (unsigned n = 0; n < hdev->nvqs; ++n) {
>>> +        VhostShadowVirtqueue *svq = vhost_svq_new();
>>> +
>>> +        if (unlikely(!svq)) {
>>> +            error_setg(errp, "Cannot create svq %u", n);
>>> +            return -1;
>>> +        }
>>> +        g_ptr_array_add(v->shadow_vqs, svq);
>>> +    }
>>> +
>>> +out:
>>> +    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;
>>> @@ -759,6 +869,10 @@ 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);
>>>
>>> @@ -770,6 +884,10 @@ 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;
>>>    }
>>>
>>>    const VhostOps vdpa_ops = {