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authorAlex Williamson <alex.williamson@redhat.com>2018-05-15 13:53:55 -0600
committerAlex Williamson <alex.williamson@redhat.com>2018-06-08 10:24:27 -0600
commit002fe996f67f4f46d8917b14cfb6e4313c20685a (patch)
tree3bec3e6fc0ffe5fee605a6680a8a9a727874df31 /Documentation
parentd59502bc0591d75feb5824c7c24faaa8ec48a7ae (diff)
vfio/mdev: Check globally for duplicate devices
When we create an mdev device, we check for duplicates against the parent device and return -EEXIST if found, but the mdev device namespace is global since we'll link all devices from the bus. We do catch this later in sysfs_do_create_link_sd() to return -EEXIST, but with it comes a kernel warning and stack trace for trying to create duplicate sysfs links, which makes it an undesirable response. Therefore we should really be looking for duplicates across all mdev parent devices, or as implemented here, against our mdev device list. Using mdev_list to prevent duplicates means that we can remove mdev_parent.lock, but in order not to serialize mdev device creation and removal globally, we add mdev_device.active which allows UUIDs to be reserved such that we can drop the mdev_list_lock before the mdev device is fully in place. Two behavioral notes; first, mdev_parent.lock had the side-effect of serializing mdev create and remove ops per parent device. This was an implementation detail, not an intentional guarantee provided to the mdev vendor drivers. Vendor drivers can trivially provide this serialization internally if necessary. Second, review comments note the new -EAGAIN behavior when the device, and in particular the remove attribute, becomes visible in sysfs. If a remove is triggered prior to completion of mdev_device_create() the user will see a -EAGAIN error. While the errno is different, receiving an error during this period is not, the previous implementation returned -ENODEV for the same condition. Furthermore, the consistency to the user is improved in the case where mdev_device_remove_ops() returns error. Previously concurrent calls to mdev_device_remove() could see the device disappear with -ENODEV and return in the case of error. Now a user would see -EAGAIN while the device is in this transitory state. Reviewed-by: Kirti Wankhede <kwankhede@nvidia.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Acked-by: Halil Pasic <pasic@linux.ibm.com> Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/vfio-mediated-device.txt5
1 files changed, 5 insertions, 0 deletions
diff --git a/Documentation/vfio-mediated-device.txt b/Documentation/vfio-mediated-device.txt
index 1b3950346532..c3f69bcaf96e 100644
--- a/Documentation/vfio-mediated-device.txt
+++ b/Documentation/vfio-mediated-device.txt
@@ -145,6 +145,11 @@ The functions in the mdev_parent_ops structure are as follows:
* create: allocate basic resources in a driver for a mediated device
* remove: free resources in a driver when a mediated device is destroyed
+(Note that mdev-core provides no implicit serialization of create/remove
+callbacks per mdev parent device, per mdev type, or any other categorization.
+Vendor drivers are expected to be fully asynchronous in this respect or
+provide their own internal resource protection.)
+
The callbacks in the mdev_parent_ops structure are as follows:
* open: open callback of mediated device