virtio-devices: vhost-user: Add support for TDX

By enabling the VIRTIO feature VIRTIO_F_IOMMU_PLATFORM for all
vhost-user devices when needed, we force the guest to use the DMA API,
making these devices compatible with TDX. By using DMA API, the guest
triggers the TDX codepath to share some of the guest memory, in
particular the virtqueues and associated buffers so that the VMM and
vhost-user backends/processes can access this memory.

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

virtio-devices/src/vhost_user/net.rs

@@ -7,7 +7,7 @@ use crate::vhost_user::vu_common_ctrl::{VhostUserConfig, VhostUserHandle};
 use crate::vhost_user::{Error, Result, VhostUserCommon};
 use crate::{
     ActivateResult, NetCtrlEpollHandler, VirtioCommon, VirtioDevice, VirtioDeviceType,
-    VirtioInterrupt, VIRTIO_F_RING_EVENT_IDX, VIRTIO_F_VERSION_1,
+    VirtioInterrupt, VIRTIO_F_IOMMU_PLATFORM, VIRTIO_F_RING_EVENT_IDX, VIRTIO_F_VERSION_1,
 };
 use crate::{GuestMemoryMmap, GuestRegionMmap};
 use net_util::{build_net_config_space, CtrlQueue, MacAddr, VirtioNetConfig};
@@ -61,10 +61,12 @@ pub struct Net {
     epoll_thread: Option<thread::JoinHandle<()>>,
     seccomp_action: SeccompAction,
     exit_evt: EventFd,
+    iommu: bool,
 }
 
 impl Net {
     /// Create a new vhost-user-net device
+    #[allow(clippy::too_many_arguments)]
     pub fn new(
         id: String,
         mac_addr: MacAddr,
@@ -73,6 +75,7 @@ impl Net {
         seccomp_action: SeccompAction,
         restoring: bool,
         exit_evt: EventFd,
+        iommu: bool,
     ) -> Result<Net> {
         let mut num_queues = vu_cfg.num_queues;
 
@@ -102,6 +105,7 @@ impl Net {
                 epoll_thread: None,
                 seccomp_action,
                 exit_evt,
+                iommu,
             });
         }
 
@@ -192,6 +196,7 @@ impl Net {
             epoll_thread: None,
             seccomp_action,
             exit_evt,
+            iommu,
         })
     }
 
@@ -248,7 +253,11 @@ impl VirtioDevice for Net {
     }
 
     fn features(&self) -> u64 {
-        self.common.avail_features
+        let mut features = self.common.avail_features;
+        if self.iommu {
+            features |= 1u64 << VIRTIO_F_IOMMU_PLATFORM;
+        }
+        features
     }
 
     fn ack_features(&mut self, value: u64) {