From db93c6fdc7dfc3786128d2aaf2086fe49bc0d858 Mon Sep 17 00:00:00 2001
From: Leander Kohler <leander.kohler@cyberus-technology.de>
Date: Tue, 31 Mar 2026 12:03:20 +0200
Subject: [PATCH] pci: Save deferred BAR reprogramming state

OVMF can reprogram PCI BARs while memory space decoding is disabled.
Cloud Hypervisor defers the corresponding BAR move in
`pending_bar_reprogram` until the PCI command register enables Memory
Space again.

That deferred state was not part of `PciConfigurationState`. A
snapshot taken in that window restored the new BAR values in PCI
config space, but lost the pending BAR relocation needed to update the
VMM-side BAR mapping.

The restore logs show guest MMIO accesses to the reprogrammed BAR
addresses `0xc0000000`, `0x100000000`, and `0x100080000` hitting
unregistered addresses. The firmware serial output shows OVMF
assigning those same BAR addresses during PCI resource allocation,
then reaching BDS, finding the mass-storage device, and failing to
boot from it.

Serialize and restore `pending_bar_reprogram` so deferred BAR moves
survive snapshot and restore.

Co-authored-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>
Co-authored-by: Julian Schindel <julian.schindel@cyberus-technology.de>
On-behalf-of: SAP leander.kohler@sap.com
Signed-off-by: Leander Kohler <leander.kohler@cyberus-technology.de>
---
 pci/src/configuration.rs | 9 ++++++++-
 pci/src/device.rs        | 3 ++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/pci/src/configuration.rs b/pci/src/configuration.rs
index 4dbd04f12..f506017b2 100644
--- a/pci/src/configuration.rs
+++ b/pci/src/configuration.rs
@@ -422,6 +422,9 @@ pub struct PciConfigurationState {
     rom_bar_used: bool,
     last_capability: Option<(usize, usize)>,
     msix_cap_reg_idx: Option<usize>,
+    // Preserve deferred BAR moves across snapshot and restore.
+    #[serde(default)]
+    pending_bar_reprogram: Vec<BarReprogrammingParams>,
 }
 
 /// Contains the configuration space of a PCI node.
@@ -557,6 +560,7 @@ impl PciConfiguration {
             rom_bar_used,
             last_capability,
             msix_cap_reg_idx,
+            pending_bar_reprogram,
         ) = if let Some(state) = state {
             (
                 state.registers.try_into().unwrap(),
@@ -567,6 +571,7 @@ impl PciConfiguration {
                 state.rom_bar_used,
                 state.last_capability,
                 state.msix_cap_reg_idx,
+                state.pending_bar_reprogram,
             )
         } else {
             let mut registers = [0u32; NUM_CONFIGURATION_REGISTERS];
@@ -606,6 +611,7 @@ impl PciConfiguration {
                 false,
                 None,
                 None,
+                Vec::new(),
             )
         };
 
@@ -619,7 +625,7 @@ impl PciConfiguration {
             last_capability,
             msix_cap_reg_idx,
             msix_config,
-            pending_bar_reprogram: Vec::new(),
+            pending_bar_reprogram,
         }
     }
 
@@ -633,6 +639,7 @@ impl PciConfiguration {
             rom_bar_used: self.rom_bar_used,
             last_capability: self.last_capability,
             msix_cap_reg_idx: self.msix_cap_reg_idx,
+            pending_bar_reprogram: self.pending_bar_reprogram.clone(),
         }
     }
 
diff --git a/pci/src/device.rs b/pci/src/device.rs
index 3c5b3315f..3a23ea777 100644
--- a/pci/src/device.rs
+++ b/pci/src/device.rs
@@ -8,6 +8,7 @@ use std::any::Any;
 use std::sync::{Arc, Barrier, Mutex};
 use std::{io, result};
 
+use serde::{Deserialize, Serialize};
 use thiserror::Error;
 use vm_allocator::{AddressAllocator, SystemAllocator};
 use vm_device::Resource;
@@ -35,7 +36,7 @@ pub enum Error {
 }
 pub type Result<T> = std::result::Result<T, Error>;
 
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Copy, Debug, Serialize, Deserialize)]
 pub struct BarReprogrammingParams {
     pub old_base: u64,
     pub new_base: u64,