vfio_assigned_device: dynamic IOMMU mapping for P2P DMA

Cargo.lock

@@ -8703,6 +8703,7 @@ dependencies = [
  "chipset_device",
  "guestmem",
  "inspect",
+ "membacking",
  "memory_range",
  "mesh",
  "pal_async",

openvmm/membacking/src/lib.rs

@@ -88,6 +88,7 @@ mod sys {
 /// On Unix, this is an empty (uninhabitable) enum.
 pub type RemoteProcess = sys::RemoteProcess;
 
+pub use mapping_manager::Mappable;
 pub use memory_manager::DeviceMemoryMapper;
 pub use memory_manager::GuestMemoryBuilder;
 pub use memory_manager::GuestMemoryClient;
@@ -97,3 +98,6 @@ pub use memory_manager::PartitionAttachError;
 pub use memory_manager::RamVisibility;
 pub use memory_manager::RamVisibilityControl;
 pub use memory_manager::SharedMemoryBacking;
+pub use region_manager::DmaMapperClient;
+pub use region_manager::DmaMapperHandle;
+pub use region_manager::DmaTarget;

openvmm/membacking/src/mapping_manager/va_mapper.rs

@@ -44,6 +44,10 @@ use std::sync::Arc;
 use std::thread::JoinHandle;
 use thiserror::Error;
 
+/// A virtual address space mapper for guest memory.
+///
+/// Maintains a reserved VA range and maps file-backed or anonymous memory
+/// into it as directed by the mapping manager.
 pub struct VaMapper {
     inner: Arc<MapperInner>,
     process: Option<RemoteProcess>,
@@ -259,14 +263,17 @@ impl VaMapper {
         self.inner.request_mapping(range, false).await
     }
 
+    /// Returns the base pointer of the VA reservation.
     pub fn as_ptr(&self) -> *mut u8 {
         self.inner.mapping.as_ptr().cast()
     }
 
+    /// Returns the length of the VA reservation in bytes.
     pub fn len(&self) -> usize {
         self.inner.mapping.len()
     }
 
+    /// Returns the remote process, if this mapper maps into a remote process.
     pub fn process(&self) -> Option<&RemoteProcess> {
         self.process.as_ref()
     }

openvmm/membacking/src/memory_manager/device_memory.rs

@@ -158,7 +158,10 @@ impl MappableGuestMemory for DeviceMemoryControl {
                     MemoryRange::try_from(gpa..gpa.wrapping_add(self.0.len as u64))
                         .map_err(|err| io::Error::new(io::ErrorKind::InvalidInput, err))?,
                     DEVICE_PRIORITY,
-                    false, // device memory cannot currently be a DMA target
+                    false, // not a DMA target: excludes device BARs from
+                           // GuestMemorySharing (vhost-user). IOMMU consumers
+                           // get notified of these mappings via the DmaMapper
+                           // path regardless of this flag.
                 )
                 .await
                 .map_err(io::Error::other)?;

openvmm/membacking/src/memory_manager/mod.rs

@@ -455,6 +455,11 @@ impl GuestMemoryManager {
         DeviceMemoryMapper::new(self.region_manager.client().clone())
     }
 
+    /// Returns a client for registering DMA mappers (VFIO, iommufd).
+    pub fn dma_mapper_client(&self) -> crate::region_manager::DmaMapperClient {
+        crate::region_manager::DmaMapperClient::new(self.region_manager.client())
+    }
+
     /// Returns an object for manipulating the visibility state of different RAM
     /// regions.
     pub fn ram_visibility_control(&self) -> RamVisibilityControl {