Fields of SysBusDevice must only be accessed with the BQL taken.  Add
a wrapper that verifies that.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 rust/hw/timer/hpet/src/hpet.rs |  4 +---
 rust/qemu-api/src/sysbus.rs    | 12 ++++++++++++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/rust/hw/timer/hpet/src/hpet.rs b/rust/hw/timer/hpet/src/hpet.rs
index ce4b289d0c8..a440c9f4cb9 100644
--- a/rust/hw/timer/hpet/src/hpet.rs
+++ b/rust/hw/timer/hpet/src/hpet.rs
@@ -724,8 +724,6 @@ fn realize(&self) {
     }
 
     fn reset_hold(&self, _type: ResetType) {
-        let sbd = self.upcast::<SysBusDevice>();
-
         for timer in self.timers.iter().take(self.num_timers.get()) {
             timer.borrow_mut().reset();
         }
@@ -738,7 +736,7 @@ fn reset_hold(&self, _type: ResetType) {
         HPETFwConfig::update_hpet_cfg(
             self.hpet_id.get(),
             self.capability.get() as u32,
-            sbd.mmio[0].addr,
+            self.mmio_addr(0).unwrap(),
         );
 
         // to document that the RTC lowers its output on reset as well
diff --git a/rust/qemu-api/src/sysbus.rs b/rust/qemu-api/src/sysbus.rs
index 48803a655f9..0790576d446 100644
--- a/rust/qemu-api/src/sysbus.rs
+++ b/rust/qemu-api/src/sysbus.rs
@@ -64,6 +64,18 @@ fn init_irq(&self, irq: &InterruptSource) {
         }
     }
 
+    // TODO: do we want a type like GuestAddress here?
+    fn mmio_addr(&self, id: u32) -> Option<u64> {
+        assert!(bql_locked());
+        let sbd = self.upcast();
+        let id: usize = id.try_into().unwrap();
+        if sbd.mmio[id].memory.is_null() {
+            None
+        } else {
+            Some(sbd.mmio[id].addr)
+        }
+    }
+
     // TODO: do we want a type like GuestAddress here?
     fn mmio_map(&self, id: u32, addr: u64) {
         assert!(bql_locked());
-- 
2.48.1

On Thu, Feb 27, 2025 at 03:22:15PM +0100, Paolo Bonzini wrote:
> Date: Thu, 27 Feb 2025 15:22:15 +0100
> From: Paolo Bonzini <pbonzini@redhat.com>
> Subject: [PATCH 08/12] rust: hpet: do not access fields of SysBusDevice
> X-Mailer: git-send-email 2.48.1
> 
> Fields of SysBusDevice must only be accessed with the BQL taken.  Add
> a wrapper that verifies that.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  rust/hw/timer/hpet/src/hpet.rs |  4 +---
>  rust/qemu-api/src/sysbus.rs    | 12 ++++++++++++
>  2 files changed, 13 insertions(+), 3 deletions(-)

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>