vm-virtio: Translate addresses for devices attached to IOMMU

In case some virtio devices are attached to the virtual IOMMU, their
vring addresses need to be translated from IOVA into GPA. Otherwise it
makes no sense to try to access them, and they would cause out of range
errors.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vm-virtio/src/device.rs

@@ -22,6 +22,9 @@ pub type VirtioInterrupt = Box<
         + Sync,
 >;
 
+pub type VirtioIommuRemapping =
+    Box<dyn Fn(u64) -> std::result::Result<u64, std::io::Error> + Send + Sync>;
+
 #[derive(Clone)]
 pub struct VirtioSharedMemory {
     pub offset: u64,
@@ -83,4 +86,18 @@ pub trait VirtioDevice: Send {
     fn get_shm_regions(&self) -> Option<VirtioSharedMemoryList> {
         None
     }
+
+    fn iommu_translate(&self, addr: u64) -> u64 {
+        addr
+    }
+}
+
+/// Trait providing address translation the same way a physical DMA remapping
+/// table would provide translation between an IOVA and a physical address.
+/// The goal of this trait is to be used by virtio devices to perform the
+/// address translation before they try to read from the guest physical address.
+/// On the other side, the implementation itself should be provided by the code
+/// emulating the IOMMU for the guest.
+pub trait DmaRemapping: Send + Sync {
+    fn translate(&self, id: u32, addr: u64) -> std::result::Result<u64, std::io::Error>;
 }