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

Hi,

On 2018/5/24 23:04, Jean-Philippe Brucker wrote:

On 24/05/18 13:35, Xu Zaibo wrote:

quoted

quoted

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);

I don't think iommu-sva.c is the best place for this, it's probably
better to implement an intermediate layer (the mediating driver), that
calls iommu_sva_device_init() and iommu_sva_device_shutdown() once. Then
vfio-pci would still call these functions itself, but for mdev the
mediating driver keeps a refcount of groups, and calls device_shutdown()
only when freeing the last mdev.

A device driver (non mdev in this example) expects to be able to free
all its resources after sva_device_shutdown() returns. Imagine the
mm_list isn't empty (mm_exit() is running late), and instead of waiting
in unbind_dev_all() below, we return 0 immediately. Then the calling
driver frees its resources, and the mm_exit callback along with private
data passed to bind() disappear. If a mm_exit() is still running in
parallel, then it will try to access freed data and corrupt memory. So
in this function if mm_list isn't empty, the only thing we can do is wait.

I still don't understand why we should 'unbind_dev_all', is it possible 
to do a 'unbind_dev_pasid'?
Then we can do other things instead of waiting that user may not like. :)

Thanks
Zaibo

quoted

+
      __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. :)

.