From a8643dc523be83066d71f6ac9e733aa543135062 Mon Sep 17 00:00:00 2001
From: Rob Bradford <robert.bradford@intel.com>
Date: Fri, 4 Dec 2020 10:17:51 +0000
Subject: [PATCH] vm-device, vmm: Wait for barrier if one is returned

Wait for the barrier if one is provided by the result of the MMIO and
PIO write.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
---
 vm-device/src/bus.rs |  8 ++++----
 vmm/src/vm.rs        | 32 ++++++++++++++++++++++++--------
 2 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/vm-device/src/bus.rs b/vm-device/src/bus.rs
index 381859319..3388ee205 100644
--- a/vm-device/src/bus.rs
+++ b/vm-device/src/bus.rs
@@ -231,13 +231,13 @@ impl Bus {
     /// Writes `data` to the device that owns the range containing `addr`.
     ///
     /// Returns true on success, otherwise `data` is untouched.
-    pub fn write(&self, addr: u64, data: &[u8]) -> Result<()> {
+    pub fn write(&self, addr: u64, data: &[u8]) -> Result<Option<Arc<Barrier>>> {
         if let Some((base, offset, dev)) = self.resolve(addr) {
             // OK to unwrap as lock() failing is a serious error condition and should panic.
-            dev.lock()
+            Ok(dev
+                .lock()
                 .expect("Failed to acquire device lock")
-                .write(base, offset, data);
-            Ok(())
+                .write(base, offset, data))
         } else {
             Err(Error::MissingAddressRange)
         }
diff --git a/vmm/src/vm.rs b/vmm/src/vm.rs
index 24703d718..0e15999bd 100644
--- a/vmm/src/vm.rs
+++ b/vmm/src/vm.rs
@@ -400,11 +400,19 @@ impl VmmOps for VmOps {
     }
 
     fn mmio_write(&self, addr: u64, data: &[u8]) -> hypervisor::vm::Result<()> {
-        if let Err(e) = self.mmio_bus.write(addr, data) {
-            if let vm_device::BusError::MissingAddressRange = e {
-                warn!("Guest MMIO write to unregistered address 0x{:x}", addr);
+        match self.mmio_bus.write(addr, data) {
+            Err(e) => {
+                if let vm_device::BusError::MissingAddressRange = e {
+                    warn!("Guest MMIO write to unregistered address 0x{:x}", addr);
+                }
             }
-        }
+            Ok(Some(barrier)) => {
+                info!("Waiting for barrier");
+                barrier.wait();
+                info!("Barrier released");
+            }
+            _ => {}
+        };
         Ok(())
     }
 
@@ -425,11 +433,19 @@ impl VmmOps for VmOps {
             return Ok(());
         }
 
-        if let Err(e) = self.io_bus.write(addr, data) {
-            if let vm_device::BusError::MissingAddressRange = e {
-                warn!("Guest PIO write to unregistered address 0x{:x}", addr);
+        match self.io_bus.write(addr, data) {
+            Err(e) => {
+                if let vm_device::BusError::MissingAddressRange = e {
+                    warn!("Guest PIO write to unregistered address 0x{:x}", addr);
+                }
             }
-        }
+            Ok(Some(barrier)) => {
+                info!("Waiting for barrier");
+                barrier.wait();
+                info!("Barrier released");
+            }
+            _ => {}
+        };
         Ok(())
     }
 }