arch, hypervisor: Report KVM IMSIC interrupt IDs

The RISC-V AIA FDT node currently advertises a fixed riscv,num-ids
value. That can diverge from the interrupt identity count configured by
KVM, which matters for guests running with an emulated IMSIC.

Record the NR_IDS value reported by KVM and expose that value through
the generated device tree. Read back the KVM-selected AIA mode without
forcing an emulation mode.

Assisted-by: OpenAI-Codex:GPT-5

Signed-off-by: wangyf0611 <wangyufeng@iscas.ac.cn>

arch/src/riscv64/fdt.rs

@@ -231,8 +231,8 @@ fn create_aia_node(fdt: &mut FdtWriter, aia_device: &Arc<Mutex<dyn Vaia>>) -> Fd
         fdt.property_u32("#interrupt-cells", 0u32)?;
         fdt.property_null("interrupt-controller")?;
         fdt.property_null("msi-controller")?;
-        // TODO complete num-ids
-        fdt.property_u32("riscv,num-ids", 2047u32)?;
+        let imsic_num_ids = aia_device.lock().unwrap().imsic_num_ids();
+        fdt.property_u32("riscv,num-ids", imsic_num_ids)?;
         fdt.property_u32("phandle", AIA_IMSIC_PHANDLE)?;
 
         let mut irq_cells = Vec::new();

hypervisor/src/arch/riscv64/aia.rs

@@ -46,6 +46,9 @@ pub trait Vaia: Send + Sync {
     /// Returns an array with IMSIC device properties
     fn imsic_properties(&self) -> [u32; 4];
 
+    /// Returns the number of IMSIC interrupt identities exposed to the guest
+    fn imsic_num_ids(&self) -> u32;
+
     /// Returns the number of vCPUs this AIA handles
     fn vcpu_count(&self) -> u32;
 

hypervisor/src/kvm/riscv64/aia.rs

@@ -24,6 +24,9 @@ pub struct KvmAiaImsics {
 
     /// Number of CPUs handled by the device
     vcpu_count: u32,
+
+    /// Number of IMSIC interrupt identities configured by KVM
+    imsic_num_ids: u32,
 }
 
 #[derive(Clone, Default, Serialize, Deserialize)]
@@ -37,20 +40,17 @@ impl KvmAiaImsics {
 
     /// Setup the device-specific attributes
     fn init_device_attributes(&mut self, nr_irqs: u32) -> Result<()> {
-        // AIA part attributes
-        // Getting the working mode of RISC-V AIA, defaults to EMUL, passible
-        // variants are EMUL, HW_ACCL, AUTO
-        let mut aia_mode = kvm_bindings::KVM_DEV_RISCV_AIA_MODE_EMUL;
+        // Read the working mode selected by KVM. Possible modes are EMUL,
+        // HW_ACCL and AUTO.
+        let mut aia_mode_readback: u32 = 0;
         Self::get_device_attribute(
             &self.device,
             kvm_bindings::KVM_DEV_RISCV_AIA_GRP_CONFIG,
             u64::from(kvm_bindings::KVM_DEV_RISCV_AIA_CONFIG_MODE),
-            &raw mut aia_mode as u64,
+            &raw mut aia_mode_readback as u64,
             0,
         )?;
 
-        // Report AIA MODE
-
         // Setting up the number of wired interrupt sources
         Self::set_device_attribute(
             &self.device,
@@ -71,6 +71,7 @@ impl KvmAiaImsics {
         )?;
 
         // Report NR_IDS
+        self.imsic_num_ids = aia_nr_ids;
 
         // Setting up hart_bits
         let max_hart_index = self.vcpu_count as u64 - 1;
@@ -191,6 +192,7 @@ impl KvmAiaImsics {
             vcpu_count: config.vcpu_count,
             aplic_addr: config.aplic_addr,
             imsic_addr: config.imsic_addr,
+            imsic_num_ids: 0,
         };
 
         aia_device.init_device_attributes(config.nr_irqs)?;
@@ -226,6 +228,10 @@ impl Vaia for KvmAiaImsics {
         ]
     }
 
+    fn imsic_num_ids(&self) -> u32 {
+        self.imsic_num_ids
+    }
+
     fn vcpu_count(&self) -> u32 {
         self.vcpu_count
     }