[RFC PATCH 6/6] vdpa_sim: add support for user VA

[Stefano Garzarella]

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 device is reset.

Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
---
 drivers/vdpa/vdpa_sim/vdpa_sim.h |   1 +
 drivers/vdpa/vdpa_sim/vdpa_sim.c | 104 ++++++++++++++++++++++++++++++-
 2 files changed, 103 insertions(+), 2 deletions(-)

diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.h b/drivers/vdpa/vdpa_sim/vdpa_sim.h
index 07ef53ea375e..1b010e5c0445 100644
--- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
+++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
@@ -55,6 +55,7 @@ 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;
 	/* spinlock to synchronize virtqueue state */
 	spinlock_t lock;
diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
index 36a1d2e0a6ba..6e07cedef30c 100644
--- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
+++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
@@ -36,10 +36,90 @@ 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;
+module_param(use_va, bool, 0444);
+MODULE_PARM_DESC(use_va, "Enable 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 task_struct *owner;
+	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);
+#if 0
+		if (mm_work->owner)
+			mm_work->ret = cgroup_attach_task_all(mm_work->owner,
+							      current);
+#endif
+	} else {
+#if 0
+		//TODO: check it
+		cgroup_release(current);
+#endif
+		kthread_unuse_mm(mm_work->mm);
+	}
+}
+
+static void vdpasim_worker_queue_mm(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);
+
+	spin_unlock(&vdpasim->lock);
+	kthread_flush_work(work);
+	spin_lock(&vdpasim->lock);
+}
+
+static int vdpasim_worker_bind_mm(struct vdpasim *vdpasim,
+				  struct mm_struct *new_mm,
+				  struct task_struct *owner)
+{
+	struct vdpasim_mm_work mm_work;
+
+	mm_work.owner = owner;
+	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;
+
+	vdpasim_worker_queue_mm(vdpasim, &mm_work);
+
+	vdpasim->mm_bound = NULL;
+}
 static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
 {
 	return container_of(vdpa, struct vdpasim, vdpa);
@@ -66,8 +146,10 @@ static void vdpasim_vq_notify(struct vringh *vring)
 static void vdpasim_queue_ready(struct vdpasim *vdpasim, unsigned int idx)
 {
 	struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
+	bool va_enabled = use_va && vdpasim->mm_bound;
 
-	vringh_init_iotlb(&vq->vring, vdpasim->features, vq->num, false, false,
+	vringh_init_iotlb(&vq->vring, vdpasim->features, vq->num, false,
+			  va_enabled,
 			  (struct vring_desc *)(uintptr_t)vq->desc_addr,
 			  (struct vring_avail *)
 			  (uintptr_t)vq->driver_addr,
@@ -96,6 +178,9 @@ static void vdpasim_do_reset(struct vdpasim *vdpasim)
 {
 	int i;
 
+	//TODO: should we cancel the works?
+	vdpasim_worker_unbind_mm(vdpasim);
+
 	spin_lock(&vdpasim->iommu_lock);
 
 	for (i = 0; i < vdpasim->dev_attr.nvqs; i++) {
@@ -275,7 +360,7 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
 
 	vdpasim = vdpa_alloc_device(struct vdpasim, vdpa, NULL, ops,
 				    dev_attr->ngroups, dev_attr->nas,
-				    dev_attr->name, false);
+				    dev_attr->name, use_va);
 	if (IS_ERR(vdpasim)) {
 		ret = PTR_ERR(vdpasim);
 		goto err_alloc;
@@ -657,6 +742,19 @@ 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 task_struct *owner)
+{
+	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
+	int ret;
+
+	spin_lock(&vdpasim->lock);
+	ret = vdpasim_worker_bind_mm(vdpasim, mm, owner);
+	spin_unlock(&vdpasim->lock);
+
+	return ret;
+}
+
 static int vdpasim_dma_map(struct vdpa_device *vdpa, unsigned int asid,
 			   u64 iova, u64 size,
 			   u64 pa, u32 perm, void *opaque)
@@ -744,6 +842,7 @@ 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,
 	.free                   = vdpasim_free,
 };
 
@@ -776,6 +875,7 @@ 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,
 	.free                   = vdpasim_free,
 };
 
-- 
2.38.1