Re: [PATCH v3 8/8] vdpa_sim: add support for user VA

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On Fri, Mar 24, 2023 at 11:49:32AM +0800, Jason Wang wrote:

在 2023/3/21 23:48, Stefano Garzarella 写道:
The new "use_va" module parameter (default: true) 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 serialize the binding to a new
address space when the .bind_mm callback is invoked, and unbinding
when the .unbind_mm callback is invoked.

Call mmget_not_zero()/kthread_use_mm() inside the worker function
to pin the address space only as long as needed, following the
documentation of mmget() in include/linux/sched/mm.h:

  * Never use this function to pin this address space for an
  * unbounded/indefinite amount of time.

Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
---

Notes:
    v3:
    - called mmget_not_zero() before kthread_use_mm() [Jason]
      As the documentation of mmget() in include/linux/sched/mm.h says:
      * Never use this function to pin this address space for an
      * unbounded/indefinite amount of time.
      I moved mmget_not_zero/kthread_use_mm inside the worker function,
      this way we pin the address space only as long as needed.
      This is similar to what vfio_iommu_type1_dma_rw_chunk() does in
      drivers/vfio/vfio_iommu_type1.c
    - simplified the mm bind/unbind [Jason]
    - renamed vdpasim_worker_change_mm_sync() [Jason]
    - fix commit message (s/default: false/default: true)
    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 | 80 +++++++++++++++++++++++++++++++-
 2 files changed, 79 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 ab4cfb82c237..23c891cdcd54 100644
--- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
+++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
@@ -35,10 +35,44 @@ 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 vdpasim *vdpasim;
+	struct mm_struct *mm_to_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);
+	struct vdpasim *vdpasim = mm_work->vdpasim;
+
+	mm_work->ret = 0;
+
+	//TODO: should we attach the cgroup of the mm owner?
+	vdpasim->mm_bound = mm_work->mm_to_bind;
+}
+
+static void vdpasim_worker_change_mm_sync(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);
+
+	kthread_flush_work(work);
+}
+
 static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
 {
 	return container_of(vdpa, struct vdpasim, vdpa);
@@ -59,8 +93,10 @@ 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,
@@ -130,8 +166,20 @@ static const struct vdpa_config_ops vdpasim_batch_config_ops;
 static void vdpasim_work_fn(struct kthread_work *work)
 {
 	struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
+	struct mm_struct *mm = vdpasim->mm_bound;
+
+	if (mm) {
+		if (!mmget_not_zero(mm))
+			return;


Do we need to check use_va here.

Yep, right!


Other than this

Acked-by: Jason Wang <jasowang@xxxxxxxxxx>

Thanks for the reviews,
Stefano

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