virtio-devices: block: Reuse descriptor chain's memory for queue enable

weltling · rbradford · commit 1db8858fac03 · 2026-06-21T19:46:46.000Z
The two synchronous completion paths add the head to the used ring with
desc_chain.memory() but reload self.mem.memory() to enable
notifications. Keep both on the snapshot the chain was parsed from so
the used ring update and the notification enable always act on one
guest memory view rather than two independent atomic loads.

Signed-off-by: Anatol Belski &lt;anbelski@linux.microsoft.com&gt;
diff --git a/virtio-devices/src/block.rs b/virtio-devices/src/block.rs
@@ -317,7 +317,7 @@ impl BlockEpollHandler {
                     .add_used(desc_chain.memory(), desc_chain.head_index(), 1)
                     .map_err(Error::QueueAddUsed)?;
                 queue
-                    .enable_notification(self.mem.memory().deref())
+                    .enable_notification(desc_chain.memory())
                     .map_err(Error::QueueEnableNotification)?;
                 continue;
             }
@@ -404,7 +404,7 @@ impl BlockEpollHandler {
                     .add_used(desc_chain.memory(), desc_chain.head_index(), len)
                     .map_err(Error::QueueAddUsed)?;
                 queue
-                    .enable_notification(self.mem.memory().deref())
+                    .enable_notification(desc_chain.memory())
                     .map_err(Error::QueueEnableNotification)?;
             }
         }

Original file line number	Diff line number	Diff line change
`@@ -317,7 +317,7 @@ impl BlockEpollHandler {`
`317`	`317`	`.add_used(desc_chain.memory(), desc_chain.head_index(), 1)`
`318`	`318`	`.map_err(Error::QueueAddUsed)?;`
`319`	`319`	`queue`
`320`		`- .enable_notification(self.mem.memory().deref())`
	`320`	`+ .enable_notification(desc_chain.memory())`
`321`	`321`	`.map_err(Error::QueueEnableNotification)?;`
`322`	`322`	`continue;`
`323`	`323`	`}`
`@@ -404,7 +404,7 @@ impl BlockEpollHandler {`
`404`	`404`	`.add_used(desc_chain.memory(), desc_chain.head_index(), len)`
`405`	`405`	`.map_err(Error::QueueAddUsed)?;`
`406`	`406`	`queue`
`407`		`- .enable_notification(self.mem.memory().deref())`
	`407`	`+ .enable_notification(desc_chain.memory())`
`408`	`408`	`.map_err(Error::QueueEnableNotification)?;`
`409`	`409`	`}`
`410`	`410`	`}`