Whenever a virtio device is placed behind a vIOMMU, we have some code in
pci_common_config.rs to translate the queue addresses (descriptor table,
available ring and used ring) from GVA to GPA, so that they can be used
correctly.
But in case of vDPA, we also need to provide the queue addresses to the
vhost backend. And since the vhost backend deals with consistent IOVAs,
all addresses being provided should be GVAs if the device is placed
being a vIOMMU. For that reason, we perform a translation of the queue
addresses back from GPA to GVA if necessary, and only to be provided to
the vhost backend.
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
Now that we rely on vhost v0.4.0, which contains the fix for
get_iova_range(), we don't need the workaround anymore, and we can
actually call into the dedicated function.
Fixes#3861
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
vDPA is a kernel framework introduced fairly recently in order to handle
devices complying with virtio specification on their datapath, while the
control path is vendor specific. For the datapath, that means the
virtqueues are handled through DMA directly between the hardware and the
guest, while the control path goes through the vDPA framework,
eventually exposed through a vhost-vdpa device.
vDPA, like VFIO, aims at achieving baremetal performance for devices
that are passed into a VM. But unlike VFIO, it provides a simpler/better
framework for achieving migration. Because the DMA accesses between the
device and the guest are going through virtio queues, migration can be
achieved way more easily, and doesn't require each device driver to
implement the migration support. In the VFIO case, each vendor is
expected to provide an implementation of the VFIO migration framework,
which makes things harder as it must be done for each and every device.
So to summarize the point is to support migration for hardware devices
through which we can achieve baremetal performances.
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>