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

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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.

Other than this

Acked-by: Jason Wang <jasowang@xxxxxxxxxx>

Thanks


+		kthread_use_mm(mm);
+	}
vdpasim->dev_attr.work_fn(vdpasim);
+
+	if (mm) {
+		kthread_unuse_mm(mm);
+		mmput(mm);
+	}
  }
struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
@@ -162,7 +210,7 @@ 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;
@@ -582,6 +630,30 @@ 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);
+	struct vdpasim_mm_work mm_work;
+
+	mm_work.vdpasim = vdpasim;
+	mm_work.mm_to_bind = mm;
+
+	vdpasim_worker_change_mm_sync(vdpasim, &mm_work);
+
+	return mm_work.ret;
+}
+
+static void vdpasim_unbind_mm(struct vdpa_device *vdpa)
+{
+	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
+	struct vdpasim_mm_work mm_work;
+
+	mm_work.vdpasim = vdpasim;
+	mm_work.mm_to_bind = NULL;
+
+	vdpasim_worker_change_mm_sync(vdpasim, &mm_work);
+}
+
  static int vdpasim_dma_map(struct vdpa_device *vdpa, unsigned int asid,
  			   u64 iova, u64 size,
  			   u64 pa, u32 perm, void *opaque)
@@ -678,6 +750,8 @@ 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,
  };
@@ -712,6 +786,8 @@ 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,
  };

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