From 5b53f4202d183c2f890d651b6281b66c1e6cd9fe Mon Sep 17 00:00:00 2001
From: Rob Bradford <rbradford@meta.com>
Date: Wed, 8 Jul 2026 12:12:13 -0700
Subject: [PATCH] vmm: Reject removal of already removed devices

A hot-unplug leaves the PCI node in the device tree until the guest
acknowledges the ejection, but VmConfig drops the device entry
immediately.

Move the config removal into DeviceManager::remove_device() and fail
when it returns false, so a second remove-device request cannot reuse
the stale device-tree node.

Assisted-by: OpenAI:Codex-GPT-5
Signed-off-by: Rob Bradford <rbradford@meta.com>
---
 vmm/src/device_manager.rs | 50 ++++++++++++++++++++++++---------------
 vmm/src/vm.rs             |  4 ----
 2 files changed, 31 insertions(+), 23 deletions(-)

diff --git a/vmm/src/device_manager.rs b/vmm/src/device_manager.rs
index ec58b86bd..416132e62 100644
--- a/vmm/src/device_manager.rs
+++ b/vmm/src/device_manager.rs
@@ -5023,20 +5023,24 @@ impl DeviceManager {
             match device_type {
                 VirtioDeviceType::Net => {
                     let mut config = self.config.lock().unwrap();
-                    let nets = config.net.as_deref_mut().unwrap();
-                    let net_dev_cfg = nets
-                        .iter_mut()
-                        .find(|net| net.pci_common.id.as_deref() == Some(id))
-                        // unwrap: the device could not have been removed without an ID
-                        .unwrap();
-                    let fds = net_dev_cfg.fds.take().unwrap_or(Vec::new());
-
-                    debug!("Closing preserved FDs from virtio-net device: id={id}, fds={fds:?}");
-                    for fd in fds {
-                        config.preserved_fds.as_mut().unwrap().remove(&fd);
-                        // SAFETY: We are closing the only remaining instance of this FD.
-                        unsafe {
-                            libc::close(fd);
+                    if let Some(fds) = config
+                        .net
+                        .as_deref_mut()
+                        .and_then(|nets| {
+                            nets.iter_mut()
+                                .find(|net| net.pci_common.id.as_deref() == Some(id))
+                        })
+                        .map(|net_dev_cfg| net_dev_cfg.fds.take().unwrap_or_default())
+                    {
+                        debug!(
+                            "Closing preserved FDs from virtio-net device: id={id}, fds={fds:?}"
+                        );
+                        for fd in fds {
+                            config.preserved_fds.as_mut().unwrap().remove(&fd);
+                            // SAFETY: We are closing the only remaining instance of this FD.
+                            unsafe {
+                                libc::close(fd);
+                            }
                         }
                     }
                 }
@@ -5050,11 +5054,15 @@ impl DeviceManager {
             // Cleanup externally-provided VFIO cdev FDs: remove the preserved
             // original from VmConfig and close it.
             let mut config = self.config.lock().unwrap();
-            if let Some(devices) = config.devices.as_deref_mut()
-                && let Some(device_cfg) = devices
-                    .iter_mut()
-                    .find(|d| d.pci_common.id.as_deref() == Some(id))
-                && let Some(fd) = device_cfg.fd.take()
+            if let Some(fd) = config
+                .devices
+                .as_deref_mut()
+                .and_then(|devices| {
+                    devices
+                        .iter_mut()
+                        .find(|d| d.pci_common.id.as_deref() == Some(id))
+                })
+                .and_then(|device_cfg| device_cfg.fd.take())
             {
                 debug!("Closing preserved FD from VFIO device: id={id}, fd={fd}");
                 let fd_removed = config.preserved_fds.as_mut().unwrap().remove(&fd);
@@ -5069,6 +5077,10 @@ impl DeviceManager {
             }
         }
 
+        if !self.config.lock().unwrap().remove_device(id) {
+            return Err(DeviceManagerError::UnknownDeviceId(id.to_string()));
+        }
+
         // Update the PCID bitmap
         self.pci_segments[pci_segment_id as usize].pci_devices_down |= 1 << pci_device_bdf.device();
 
diff --git a/vmm/src/vm.rs b/vmm/src/vm.rs
index effcd988d..3bcb5a34d 100644
--- a/vmm/src/vm.rs
+++ b/vmm/src/vm.rs
@@ -2236,10 +2236,6 @@ impl Vm {
             .remove_device(id)
             .map_err(Error::DeviceManager)?;
 
-        // Update VmConfig by removing the device. This is important to
-        // ensure the device would not be created in case of a reboot.
-        self.config.lock().unwrap().remove_device(id);
-
         self.device_manager
             .lock()
             .unwrap()