Re: [PATCH v2 13/40] vfio: Add support for Shared Virtual Addressing

[Xu Zaibo <xuzaibo@xxxxxxxxxx>]

On 2018/5/24 19:44, Jean-Philippe Brucker wrote:

Hi,

On 23/05/18 10:38, Xu Zaibo wrote:

+static int vfio_iommu_bind_group(struct vfio_iommu *iommu,
+                 struct vfio_group *group,
+                 struct vfio_mm *vfio_mm)
+{
+    int ret;
+    bool enabled_sva = false;
+    struct vfio_iommu_sva_bind_data data = {
+        .vfio_mm    = vfio_mm,
+        .iommu        = iommu,
+        .count        = 0,
+    };
+
+    if (!group->sva_enabled) {
+        ret = iommu_group_for_each_dev(group->iommu_group, NULL,
+                           vfio_iommu_sva_init);

Do we need to do *sva_init here or do anything to avoid repeated
initiation?
while another process already did initiation at this device, I think
that current process will get an EEXIST.

Right, sva_init() must be called once for any device that intends to use
bind(). For the second process though, group->sva_enabled will be true
so we won't call sva_init() again, only bind().

Well, while I create mediated devices based on one parent device to support multiple
processes(a new process will create a new 'vfio_group' for the corresponding mediated device,
and 'sva_enabled' cannot work any more), in fact, *sva_init and *sva_shutdown are basically
working on parent device, so, as a result, I just only need sva initiation and shutdown on the
parent device only once. So I change the two as following:

@@ -551,8 +565,18 @@ int iommu_sva_device_init(struct device *dev, unsigned long features,
      if (features & ~IOMMU_SVA_FEAT_IOPF)
         return -EINVAL;

+    /* If already exists, do nothing  */
+    mutex_lock(&dev->iommu_param->lock);
+    if (dev->iommu_param->sva_param) {
+        mutex_unlock(&dev->iommu_param->lock);
+        return 0;
+    }
+    mutex_unlock(&dev->iommu_param->lock);
 
     if (features & IOMMU_SVA_FEAT_IOPF) {
         ret = iommu_register_device_fault_handler(dev, iommu_queue_iopf,


@@ -621,6 +646,14 @@ int iommu_sva_device_shutdown(struct device *dev)
     if (!domain)
         return -ENODEV;
 
+    /* If any other process is working on the device, shut down does nothing. */
+    mutex_lock(&dev->iommu_param->lock);
+    if (!list_empty(&dev->iommu_param->sva_param->mm_list)) {
+        mutex_unlock(&dev->iommu_param->lock);
+        return 0;
+    }
+    mutex_unlock(&dev->iommu_param->lock);
+
     __iommu_sva_unbind_dev_all(dev);
 
     mutex_lock(&dev->iommu_param->lock);

I add the above two checkings in both *sva_init and *sva_shutdown, it is working now,
but i don't know if it will cause any new problems. What's more, i doubt if it is
reasonable to check this to avoid repeating operation in VFIO, maybe it is better to check
in IOMMU. :)

Thanks
Zaibo

.