From c3f1c3ee3df276c3e416845e67542aed146f142c Mon Sep 17 00:00:00 2001
From: Alexandru Matei <alexandru.matei@uipath.com>
Date: Fri, 22 Mar 2024 13:49:08 +0200
Subject: [PATCH] virtio-devices: save pci configuration capability state in
 snapshot

When restoring a VM, the VirtioPciCfgCapInfo struct is not properly
initialized. All fields are 0, including the offset where the
capabibility starts. Hence, when you read a PCI configuration register
in the range [0..length(VirtioPciCfgCap)] you get the value 0 instead of
the actual register contents.

Linux rescans the whole PCI bus when adding a new device. It reads the
values vendor_id and device_id for every device. Because these are
stored at offset 0 in pci configuration space, their value is 0 for
existing devices.  As such, Linux considers that the devices have been
unplugged and it removes them from the system.

Fixes: #6265

Signed-off-by: Alexandru Matei <alexandru.matei@uipath.com>
---
 virtio-devices/src/transport/pci_device.rs | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/virtio-devices/src/transport/pci_device.rs b/virtio-devices/src/transport/pci_device.rs
index 931d722d5..58e79ae33 100644
--- a/virtio-devices/src/transport/pci_device.rs
+++ b/virtio-devices/src/transport/pci_device.rs
@@ -278,6 +278,8 @@ pub struct VirtioPciDeviceState {
     device_activated: bool,
     queues: Vec<QueueState>,
     interrupt_status: usize,
+    cap_pci_cfg_offset: usize,
+    cap_pci_cfg: Vec<u8>,
 }
 
 impl VersionMapped for VirtioPciDeviceState {}
@@ -530,7 +532,7 @@ impl VirtioPciDevice {
                 ))
             })?;
 
-        let (device_activated, interrupt_status) = if let Some(state) = state {
+        let (device_activated, interrupt_status, cap_pci_cfg_info) = if let Some(state) = state {
             // Update virtqueues indexes for both available and used rings.
             for (i, queue) in queues.iter_mut().enumerate() {
                 queue.set_size(state.queues[i].size);
@@ -558,9 +560,16 @@ impl VirtioPciDevice {
                 );
             }
 
-            (state.device_activated, state.interrupt_status)
+            (
+                state.device_activated,
+                state.interrupt_status,
+                VirtioPciCfgCapInfo {
+                    offset: state.cap_pci_cfg_offset,
+                    cap: *VirtioPciCfgCap::from_slice(&state.cap_pci_cfg).unwrap(),
+                },
+            )
         } else {
-            (false, 0)
+            (false, 0, VirtioPciCfgCapInfo::default())
         };
 
         // Dropping the MutexGuard to unlock the VirtioDevice. This is required
@@ -585,7 +594,7 @@ impl VirtioPciDevice {
             settings_bar: 0,
             use_64bit_bar,
             interrupt_source_group,
-            cap_pci_cfg_info: VirtioPciCfgCapInfo::default(),
+            cap_pci_cfg_info,
             bar_regions: vec![],
             activate_evt,
             dma_handler,
@@ -634,6 +643,8 @@ impl VirtioPciDevice {
                     used_ring: q.used_ring(),
                 })
                 .collect(),
+            cap_pci_cfg_offset: self.cap_pci_cfg_info.offset,
+            cap_pci_cfg: self.cap_pci_cfg_info.cap.bytes().to_vec(),
         }
     }