vmm: retrieve timebase-frequency from KVM instead of hardcoding

The RISC-V device tree's timebase-frequency was hardcoded to 10 MHz
(0x989680). Actual hardware uses different frequencies.

Read the timebase frequency from KVM_GET_ONE_REG via
KVM_REG_RISCV_TIMER (offset 0, kvm_riscv_timer.frequency),
thread it through the VMM to arch to FDT layers, and fall back to
the 10 MHz default when KVM returns no value.

Signed-off-by: Meng Zhuo <mengzhuo@iscas.ac.cn>

vmm/src/cpu.rs

@@ -642,6 +642,11 @@ impl Vcpu {
         self.vcpu.run()
     }
 
+    #[cfg(target_arch = "riscv64")]
+    pub fn get_timebase_frequency(&self) -> result::Result<u64, hypervisor::HypervisorCpuError> {
+        self.vcpu.get_timebase_frequency()
+    }
+
     #[cfg(feature = "sev_snp")]
     pub fn set_sev_control_register(&self, vmsa_pfn: u64) -> Result<()> {
         self.vcpu

vmm/src/vm.rs

@@ -1988,6 +1988,16 @@ impl Vm {
 
         // TODO: PMU support for riscv64 is scheduled to next stage.
 
+        let timebase_frequency = self
+            .cpu_manager
+            .lock()
+            .unwrap()
+            .vcpus()
+            .first()
+            .and_then(|vcpu| vcpu.lock().unwrap().get_timebase_frequency().ok())
+            .map(|f| f as u32)
+            .unwrap_or(0x989680);
+
         arch::configure_system(
             &mem,
             cmdline.as_cstring().unwrap().to_str().unwrap(),
@@ -1996,6 +2006,7 @@ impl Vm {
             &initramfs_config,
             &pci_space_info,
             &vaia,
+            timebase_frequency,
         )
         .map_err(Error::ConfigureSystem)?;