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vmm: cpu: Retry sending signals if necessary

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To avoid a race condition where the signal might "miss" the KVM_RUN
ioctl() instead reapeatedly try sending a signal until the vCPU run is
interrupted (as indicated by setting a new per vCPU atomic.)

It important to also clear this atomic when coming out of a paused
state.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
This commit is contained in:
Rob Bradford 2020-05-06 11:34:19 +01:00 committed by Sebastien Boeuf
parent 31bde4f5da
commit 12e00c0f45
1 changed files with 24 additions and 4 deletions
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28
vmm/src/cpu.rs
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@ -664,6 +664,7 @@ struct VcpuState {
removing: bool,
handle: Option<thread::JoinHandle<()>>,
kill: Arc<AtomicBool>,
vcpu_run_interrupted: Arc<AtomicBool>,
}
impl VcpuState {
@ -673,8 +674,17 @@ impl VcpuState {
fn signal_thread(&self) {
if let Some(handle) = self.handle.as_ref() {
unsafe {
libc::pthread_kill(handle.as_pthread_t() as _, SIGRTMIN());
loop {
unsafe {
libc::pthread_kill(handle.as_pthread_t() as _, SIGRTMIN());
}
if self.vcpu_run_interrupted.load(Ordering::SeqCst) {
break;
} else {
// This is more effective than thread::yield_now() at
// avoiding a priority inversion with the vCPU thread
thread::sleep(std::time::Duration::from_millis(1));
}
}
}
}
@ -806,6 +816,9 @@ impl CpuManager {
let vcpu_pause_signalled = self.vcpus_pause_signalled.clone();
let vcpu_kill = self.vcpu_states[usize::from(cpu_id)].kill.clone();
let vcpu_run_interrupted = self.vcpu_states[usize::from(cpu_id)]
.vcpu_run_interrupted
.clone();
if let Some(snapshot) = snapshot {
let mut cpuid = self.cpuid.clone();
@ -854,6 +867,7 @@ impl CpuManager {
}
Ok(true) => {}
Ok(false) => {
vcpu_run_interrupted.store(true, Ordering::SeqCst);
reset_evt.write(1).unwrap();
break;
}
@ -863,6 +877,7 @@ impl CpuManager {
if vcpu_kill_signalled.load(Ordering::SeqCst)
|| vcpu_kill.load(Ordering::SeqCst)
{
vcpu_run_interrupted.store(true, Ordering::SeqCst);
break;
}
@ -873,14 +888,19 @@ impl CpuManager {
// We enter a loop because park() could spuriously
// return. We will then park() again unless the
// pause boolean has been toggled.
while vcpu_pause_signalled.load(Ordering::SeqCst) {
thread::park();
if vcpu_pause_signalled.load(Ordering::SeqCst) {
vcpu_run_interrupted.store(true, Ordering::SeqCst);
while vcpu_pause_signalled.load(Ordering::SeqCst) {
thread::park();
}
vcpu_run_interrupted.store(false, Ordering::SeqCst);
}
// We've been told to terminate
if vcpu_kill_signalled.load(Ordering::SeqCst)
|| vcpu_kill.load(Ordering::SeqCst)
{
vcpu_run_interrupted.store(true, Ordering::SeqCst);
break;
}
}