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

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

On Thu, Mar 2, 2023 at 7:35 PM Stefano Garzarella [off-list ref] wrote:

quoted

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@redhat.com>
---

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.

quoted

+       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?

quoted

+
+       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