PVM: no-KVM Firecracker support on latest upstream

Author: dylanwongtencent

src/vmm/src/arch/x86_64/vcpu.rs

@@ -640,8 +640,12 @@ impl KvmVcpu {
     }
 
     /// Scale the TSC frequency of this vCPU to the one provided as a parameter.
-    pub fn set_tsc_khz(&self, tsc_freq: u32) -> Result<(), SetTscError> {
-        self.fd.set_tsc_khz(tsc_freq).map_err(SetTscError)
+    pub fn set_tsc_khz(&self, _: u32) -> Result<(), SetTscError> {
+        // Disable TSC scaling when using PVM because it is unsupported on most virtualized platforms.
+        // Even on supported platforms like virtualized AMD CPUs, enabling TSC scaling can cause VM freezes
+        // after resuming from a snapshot.
+        // For more details, see https://github.com/virt-pvm/linux/issues/12#issue-2515360332
+        Ok(())
     }
 
     /// Use provided state to populate KVM internal state.

src/vmm/src/cpu_config/x86_64/custom_cpu_template.rs

@@ -39,7 +39,8 @@ impl GetCpuTemplate for Option<CpuTemplateType> {
 
                     let cpu_model = CpuModel::get_cpu_model();
                     if !template.get_supported_cpu_models().contains(&cpu_model) {
-                        return Err(InvalidCpuModel);
+                        // Disable the CPU compatibility check to allow using templates like T2A on more modern CPUs
+                        // return Err(InvalidCpuModel);
                     }
 
                     match template {