[WIP] fix(vmm): call KVMCLOCK_CTRL when pausing

resources/seccomp/x86_64-unknown-linux-musl.json

@@ -1238,6 +1238,18 @@
                     }
                 ]
             },
+            {
+                "syscall": "ioctl",
+                "args": [
+                    {
+                        "index": 1,
+                        "type": "dword",
+                        "op": "eq",
+                        "val": 44717,
+                        "comment": "KVM_KVMCLOCK_CTRL"
+                    }
+                ]
+            },
             {
                 "syscall": "sched_yield",
                 "comment": "Used by the rust standard library in std::sync::mpmc. Firecracker uses mpsc channels from this module for inter-thread communication"

src/vmm/src/vstate/vcpu/mod.rs

@@ -16,6 +16,8 @@ use std::{fmt, io, thread};
 use kvm_bindings::{KVM_SYSTEM_EVENT_RESET, KVM_SYSTEM_EVENT_SHUTDOWN};
 use kvm_ioctls::VcpuExit;
 use libc::{c_int, c_void, siginfo_t};
+#[cfg(target_arch = "x86_64")]
+use log::warn;
 use log::{error, info};
 use seccompiler::{BpfProgram, BpfProgramRef};
 use utils::errno;
@@ -296,8 +298,15 @@ impl Vcpu {
                     .send(VcpuResponse::Paused)
                     .expect("vcpu channel unexpectedly closed");
 
-                // TODO: we should call `KVM_KVMCLOCK_CTRL` here to make sure
-                // TODO continued: the guest soft lockup watchdog does not panic on Resume.
+                // Calling `KVM_KVMCLOCK_CTRL` to make sure the guest softlockup watchdog
+                // does not panic on resume, see https://docs.kernel.org/virt/kvm/api.html .
+                // We do not want to fail if the call is not successful, because depending
+                // that may be acceptable depending on the workload.
+                // TODO: add a metric
+                #[cfg(target_arch = "x86_64")]
+                if let Err(err) = self.kvm_vcpu.fd.kvmclock_ctrl() {
+                    warn!("KVM_KVMCLOCK_CTRL call failed {}", err);
+                }
 
                 // Move to 'paused' state.
                 state = StateMachine::next(Self::paused);