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

[Stefano Garzarella]

On Tue, Mar 14, 2023 at 01:36:13PM +0800, Jason Wang wrote:
> 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.

Yep, or split in 2 functions.

> > +       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?

Yep, I need to put `vdpasim` in struct vdpasim_mm_work.

I'll do in the next version.

Thanks,
Stefano