pci: rollback BAR address on failed move_bar

When BAR reprogramming is detected, detect_bar_reprogramming()
eagerly updates the BAR address in config space before the actual
MMIO remapping occurs. If the subsequent move_bar() fails (e.g.
the new address falls outside the allocator range), the config
register retains the new address while the MMIO bus still uses
the old one, leaving the device broken.

Add restore_bar_addr() to undo the config space update when
move_bar() fails, so the device remains functional at its
original address.

For 64-bit BARs, restore both the low and high BAR slots as well
as the corresponding config registers, mirroring the two-slot
update logic in detect_bar_reprogramming().

Implement restore_bar_addr() for all PciDevice implementations
(VirtioPciDevice, VfioPciDevice, VfioUserPciDevice, IvshmemDevice,
PvPanicDevice, and PvmemcontrolPciDevice) by delegating to their
respective PciConfiguration::restore_bar_addr().

Signed-off-by: CMGS <ilskdw@gmail.com>

pci/src/device.rs

@@ -93,6 +93,10 @@ pub trait PciDevice: Send {
     fn move_bar(&mut self, _old_base: u64, _new_base: u64) -> result::Result<(), io::Error> {
         Ok(())
     }
+    /// Restore BAR address in config space after a failed move_bar.
+    /// This rolls back the address update made by detect_bar_reprogramming()
+    /// so that the config register stays consistent with the MMIO bus mapping.
+    fn restore_bar_addr(&mut self, _params: &BarReprogrammingParams) {}
     /// Provides a mutable reference to the Any trait. This is useful to let
     /// the caller have access to the underlying type behind the trait.
     fn as_any_mut(&mut self) -> &mut dyn Any;