Re: [PATCH v2 8/8] vdpa_sim: add support for user VA

[Jason Wang]

On Thu, Mar 2, 2023 at 7:35 PM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote:
>
> The new "use_va" module parameter (default: false) is used in
> 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 .unbind_mm callback is invoked.
>
> Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> ---
>
> Notes:
>     v2:
>     - `use_va` set to true by default [Eugenio]
>     - supported the new unbind_mm callback [Jason]
>     - removed the unbind_mm call in vdpasim_do_reset() [Jason]
>     - avoided to release the lock while call kthread_flush_work() since we
>       are now using a mutex to protect the device state
>
>  drivers/vdpa/vdpa_sim/vdpa_sim.h |  1 +
>  drivers/vdpa/vdpa_sim/vdpa_sim.c | 98 +++++++++++++++++++++++++++++++-
>  2 files changed, 97 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.h b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> index 4774292fba8c..3a42887d05d9 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> @@ -59,6 +59,7 @@ 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;
>         /* mutex to synchronize virtqueue state */
>         struct mutex mutex;
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index a28103a67ae7..eda26bc33df5 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -35,10 +35,77 @@ 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 = true;
> +module_param(use_va, bool, 0444);
> +MODULE_PARM_DESC(use_va, "Enable/disable 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 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);
> +               //TODO: should we attach the cgroup of the mm owner?
> +       } else {
> +               kthread_unuse_mm(mm_work->mm);
> +       }
> +}
> +
> +static void vdpasim_worker_queue_mm(struct vdpasim *vdpasim,
> +                                   struct vdpasim_mm_work *mm_work)
> +{

Nit: we need to tweak the name as it does flush besides queuing the work.

> +       struct kthread_work *work = &mm_work->work;
> +
> +       kthread_init_work(work, vdpasim_mm_work_fn);
> +       kthread_queue_work(vdpasim->worker, work);
> +
> +       kthread_flush_work(work);
> +}
> +
> +static int vdpasim_worker_bind_mm(struct vdpasim *vdpasim,
> +                                 struct mm_struct *new_mm)
> +{
> +       struct vdpasim_mm_work mm_work;
> +
> +       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;

Can we simply use mm_work.mm = NULL for unbinding?

> +
> +       vdpasim_worker_queue_mm(vdpasim, &mm_work);
> +
> +       vdpasim->mm_bound = NULL;

And change the mm_bound in the worker?

Thanks

> +}
>  static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
>  {
>         return container_of(vdpa, struct vdpasim, vdpa);
> @@ -59,8 +126,10 @@ static void vdpasim_queue_ready(struct vdpasim *vdpasim, unsigned int idx)
>  {
>         struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
>         uint16_t last_avail_idx = vq->vring.last_avail_idx;
> +       bool va_enabled = use_va && vdpasim->mm_bound;
>
> -       vringh_init_iotlb(&vq->vring, vdpasim->features, vq->num, true, false,
> +       vringh_init_iotlb(&vq->vring, vdpasim->features, vq->num, true,
> +                         va_enabled,
>                           (struct vring_desc *)(uintptr_t)vq->desc_addr,
>                           (struct vring_avail *)
>                           (uintptr_t)vq->driver_addr,
> @@ -151,7 +220,7 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
>         vdpa = __vdpa_alloc_device(NULL, ops,
>                                    dev_attr->ngroups, dev_attr->nas,
>                                    dev_attr->alloc_size,
> -                                  dev_attr->name, false);
> +                                  dev_attr->name, use_va);
>         if (IS_ERR(vdpa)) {
>                 ret = PTR_ERR(vdpa);
>                 goto err_alloc;
> @@ -571,6 +640,27 @@ 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 vdpasim *vdpasim = vdpa_to_sim(vdpa);
> +       int ret;
> +
> +       mutex_lock(&vdpasim->mutex);
> +       ret = vdpasim_worker_bind_mm(vdpasim, mm);
> +       mutex_unlock(&vdpasim->mutex);
> +
> +       return ret;
> +}
> +
> +static void vdpasim_unbind_mm(struct vdpa_device *vdpa)
> +{
> +       struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> +
> +       mutex_lock(&vdpasim->mutex);
> +       vdpasim_worker_unbind_mm(vdpasim);
> +       mutex_unlock(&vdpasim->mutex);
> +}
> +
>  static int vdpasim_dma_map(struct vdpa_device *vdpa, unsigned int asid,
>                            u64 iova, u64 size,
>                            u64 pa, u32 perm, void *opaque)
> @@ -667,6 +757,8 @@ 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,
> +       .unbind_mm              = vdpasim_unbind_mm,
>         .free                   = vdpasim_free,
>  };
>
> @@ -701,6 +793,8 @@ 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,
> +       .unbind_mm              = vdpasim_unbind_mm,
>         .free                   = vdpasim_free,
>  };
>
> --
> 2.39.2
>