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References: <20221214163025.103075-1-sgarzare@redhat.com> <20221214163025.103075-7-sgarzare@redhat.com>
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From:   Eugenio Perez Martin <eperezma@redhat.com>
Date:   Wed, 21 Dec 2022 08:17:41 +0100
Message-ID: <CAJaqyWdwa5P6hXJ5Ovup+Uz3293Asr10CLvi4JVQZqDL-M1p1A@mail.gmail.com>
Subject: Re: [RFC PATCH 6/6] vdpa_sim: add support for user VA
To:     Stefano Garzarella <sgarzare@redhat.com>
Cc:     virtualization@lists.linux-foundation.org,
        Jason Wang <jasowang@redhat.com>,
        Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        "Michael S. Tsirkin" <mst@redhat.com>, stefanha@redhat.com,
        netdev@vger.kernel.org
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On Wed, Dec 14, 2022 at 5:31 PM Stefano Garzarella <sgarzare@redhat.com> wrote:
>
> The new "use_va" module parameter (default: false) is used in

Why not true by default? I'd say it makes more sense for the simulator
to use va mode and only use pa for testing it.

> vdpa_alloc_device() to inform the vDPA framework that the device
> supports VA.
>
> vringh is initialized to use VA only when "use_va" is true and the
> user's mm has been bound. So, only when the bus supports user VA
> (e.g. vhost-vdpa).
>
> vdpasim_mm_work_fn work is used to attach the kthread to the user
> address space when the .bind_mm callback is invoked, and to detach
> it when the device is reset.
>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>  drivers/vdpa/vdpa_sim/vdpa_sim.h |   1 +
>  drivers/vdpa/vdpa_sim/vdpa_sim.c | 104 ++++++++++++++++++++++++++++++-
>  2 files changed, 103 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.h b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> index 07ef53ea375e..1b010e5c0445 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> @@ -55,6 +55,7 @@ struct vdpasim {
>         struct vdpasim_virtqueue *vqs;
>         struct kthread_worker *worker;
>         struct kthread_work work;
> +       struct mm_struct *mm_bound;
>         struct vdpasim_dev_attr dev_attr;
>         /* spinlock to synchronize virtqueue state */
>         spinlock_t lock;
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index 36a1d2e0a6ba..6e07cedef30c 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -36,10 +36,90 @@ module_param(max_iotlb_entries, int, 0444);
>  MODULE_PARM_DESC(max_iotlb_entries,
>                  "Maximum number of iotlb entries for each address space. 0 means unlimited. (default: 2048)");
>
> +static bool use_va;
> +module_param(use_va, bool, 0444);
> +MODULE_PARM_DESC(use_va, "Enable the device's ability to use VA");
> +
>  #define VDPASIM_QUEUE_ALIGN PAGE_SIZE
>  #define VDPASIM_QUEUE_MAX 256
>  #define VDPASIM_VENDOR_ID 0
>
> +struct vdpasim_mm_work {
> +       struct kthread_work work;
> +       struct task_struct *owner;
> +       struct mm_struct *mm;
> +       bool bind;
> +       int ret;
> +};
> +
> +static void vdpasim_mm_work_fn(struct kthread_work *work)
> +{
> +       struct vdpasim_mm_work *mm_work =
> +               container_of(work, struct vdpasim_mm_work, work);
> +
> +       mm_work->ret = 0;
> +
> +       if (mm_work->bind) {
> +               kthread_use_mm(mm_work->mm);
> +#if 0
> +               if (mm_work->owner)
> +                       mm_work->ret = cgroup_attach_task_all(mm_work->owner,
> +                                                             current);
> +#endif
> +       } else {
> +#if 0
> +               //TODO: check it
> +               cgroup_release(current);
> +#endif
> +               kthread_unuse_mm(mm_work->mm);
> +       }
> +}
> +
> +static void vdpasim_worker_queue_mm(struct vdpasim *vdpasim,
> +                                   struct vdpasim_mm_work *mm_work)
> +{
> +       struct kthread_work *work = &mm_work->work;
> +
> +       kthread_init_work(work, vdpasim_mm_work_fn);
> +       kthread_queue_work(vdpasim->worker, work);
> +
> +       spin_unlock(&vdpasim->lock);
> +       kthread_flush_work(work);
> +       spin_lock(&vdpasim->lock);
> +}
> +
> +static int vdpasim_worker_bind_mm(struct vdpasim *vdpasim,
> +                                 struct mm_struct *new_mm,
> +                                 struct task_struct *owner)
> +{
> +       struct vdpasim_mm_work mm_work;
> +
> +       mm_work.owner = owner;
> +       mm_work.mm = new_mm;
> +       mm_work.bind = true;
> +
> +       vdpasim_worker_queue_mm(vdpasim, &mm_work);
> +
> +       if (!mm_work.ret)
> +               vdpasim->mm_bound = new_mm;
> +
> +       return mm_work.ret;
> +}
> +
> +static void vdpasim_worker_unbind_mm(struct vdpasim *vdpasim)
> +{
> +       struct vdpasim_mm_work mm_work;
> +
> +       if (!vdpasim->mm_bound)
> +               return;
> +
> +       mm_work.mm = vdpasim->mm_bound;
> +       mm_work.bind = false;
> +
> +       vdpasim_worker_queue_mm(vdpasim, &mm_work);
> +
> +       vdpasim->mm_bound = NULL;
> +}
>  static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
>  {
>         return container_of(vdpa, struct vdpasim, vdpa);
> @@ -66,8 +146,10 @@ static void vdpasim_vq_notify(struct vringh *vring)
>  static void vdpasim_queue_ready(struct vdpasim *vdpasim, unsigned int idx)
>  {
>         struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
> +       bool va_enabled = use_va && vdpasim->mm_bound;
>
> -       vringh_init_iotlb(&vq->vring, vdpasim->features, vq->num, false, false,
> +       vringh_init_iotlb(&vq->vring, vdpasim->features, vq->num, false,
> +                         va_enabled,
>                           (struct vring_desc *)(uintptr_t)vq->desc_addr,
>                           (struct vring_avail *)
>                           (uintptr_t)vq->driver_addr,
> @@ -96,6 +178,9 @@ static void vdpasim_do_reset(struct vdpasim *vdpasim)
>  {
>         int i;
>
> +       //TODO: should we cancel the works?
> +       vdpasim_worker_unbind_mm(vdpasim);
> +
>         spin_lock(&vdpasim->iommu_lock);
>
>         for (i = 0; i < vdpasim->dev_attr.nvqs; i++) {
> @@ -275,7 +360,7 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
>
>         vdpasim = vdpa_alloc_device(struct vdpasim, vdpa, NULL, ops,
>                                     dev_attr->ngroups, dev_attr->nas,
> -                                   dev_attr->name, false);
> +                                   dev_attr->name, use_va);
>         if (IS_ERR(vdpasim)) {
>                 ret = PTR_ERR(vdpasim);
>                 goto err_alloc;
> @@ -657,6 +742,19 @@ static int vdpasim_set_map(struct vdpa_device *vdpa, unsigned int asid,
>         return ret;
>  }
>
> +static int vdpasim_bind_mm(struct vdpa_device *vdpa, struct mm_struct *mm,
> +                          struct task_struct *owner)
> +{
> +       struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> +       int ret;
> +
> +       spin_lock(&vdpasim->lock);
> +       ret = vdpasim_worker_bind_mm(vdpasim, mm, owner);
> +       spin_unlock(&vdpasim->lock);
> +
> +       return ret;
> +}
> +
>  static int vdpasim_dma_map(struct vdpa_device *vdpa, unsigned int asid,
>                            u64 iova, u64 size,
>                            u64 pa, u32 perm, void *opaque)
> @@ -744,6 +842,7 @@ static const struct vdpa_config_ops vdpasim_config_ops = {
>         .set_group_asid         = vdpasim_set_group_asid,
>         .dma_map                = vdpasim_dma_map,
>         .dma_unmap              = vdpasim_dma_unmap,
> +       .bind_mm                = vdpasim_bind_mm,
>         .free                   = vdpasim_free,
>  };
>
> @@ -776,6 +875,7 @@ static const struct vdpa_config_ops vdpasim_batch_config_ops = {
>         .get_iova_range         = vdpasim_get_iova_range,
>         .set_group_asid         = vdpasim_set_group_asid,
>         .set_map                = vdpasim_set_map,
> +       .bind_mm                = vdpasim_bind_mm,
>         .free                   = vdpasim_free,
>  };
>
> --
> 2.38.1
>