If a vcpu has issued a HLT instruction with interrupts disabled then it sleeps

forever in vm_handle_hlt().

This is usually not an issue as long as one of the other vcpus properly resets
or powers off the virtual machine. However, if the bhyve(8) process is killed
with a signal the halted vcpu cannot be woken up because it's sleep cannot be
interrupted.

Fix this by waking up periodically and returning from vm_handle_hlt() if
TDF_ASTPENDING is set.

Reported by:	Leon Dang
Sponsored by:	Nahanni Systems

3 files changed, 18 insertions, 2 deletions

diff --git a/sys/amd64/include/vmm.h b/sys/amd64/include/vmm.h
index 62af240..63a9b3f 100644
--- a/sys/amd64/include/vmm.h
+++ b/sys/amd64/include/vmm.h
@@ -270,6 +270,14 @@ vcpu_is_running(struct vm *vm, int vcpu, int *hostcpu)
 	return (vcpu_get_state(vm, vcpu, hostcpu) == VCPU_RUNNING);
 }
 
+#ifdef _SYS_PROC_H_
+static int __inline
+vcpu_should_yield(struct vm *vm, int vcpu)
+{
+	return (curthread->td_flags & (TDF_ASTPENDING | TDF_NEEDRESCHED));
+}
+#endif
+
 void *vcpu_stats(struct vm *vm, int vcpu);
 void vcpu_notify_event(struct vm *vm, int vcpuid, bool lapic_intr);
 struct vmspace *vm_get_vmspace(struct vm *vm);
diff --git a/sys/amd64/vmm/intel/vmx.c b/sys/amd64/vmm/intel/vmx.c
index 4f82ea6..54b2998 100644
--- a/sys/amd64/vmm/intel/vmx.c
+++ b/sys/amd64/vmm/intel/vmx.c
@@ -2559,7 +2559,7 @@ vmx_run(void *arg, int vcpu, register_t startrip, pmap_t pmap,
 			break;
 		}
 
-		if (curthread->td_flags & (TDF_ASTPENDING | TDF_NEEDRESCHED)) {
+		if (vcpu_should_yield(vm, vcpu)) {
 			enable_intr();
 			vm_exit_astpending(vmx->vm, vcpu, vmcs_guest_rip());
 			vmx_astpending_trace(vmx, vcpu, vmexit->rip);
diff --git a/sys/amd64/vmm/vmm.c b/sys/amd64/vmm/vmm.c
index 78aefc4..397035a 100644
--- a/sys/amd64/vmm/vmm.c
+++ b/sys/amd64/vmm/vmm.c
@@ -1105,6 +1105,10 @@ vm_handle_hlt(struct vm *vm, int vcpuid, bool intr_disabled, bool *retu)
 			}
 		}
 
+		/* Don't go to sleep if the vcpu thread needs to yield */
+		if (vcpu_should_yield(vm, vcpuid))
+			break;
+
 		/*
 		 * Some Linux guests implement "halt" by having all vcpus
 		 * execute HLT with interrupts disabled. 'halted_cpus' keeps
@@ -1128,7 +1132,11 @@ vm_handle_hlt(struct vm *vm, int vcpuid, bool intr_disabled, bool *retu)
 
 		t = ticks;
 		vcpu_require_state_locked(vcpu, VCPU_SLEEPING);
-		msleep_spin(vcpu, &vcpu->mtx, wmesg, 0);
+		/*
+		 * XXX msleep_spin() cannot be interrupted by signals so
+		 * wake up periodically to check pending signals.
+		 */
+		msleep_spin(vcpu, &vcpu->mtx, wmesg, hz);
 		vcpu_require_state_locked(vcpu, VCPU_FROZEN);
 		vmm_stat_incr(vm, vcpuid, VCPU_IDLE_TICKS, ticks - t);
 	}