From 85b27a9f8f0c04f10f16a93e848efb926a391638 Mon Sep 17 00:00:00 2001 From: Yong He Date: Tue, 2 Jul 2019 22:02:15 -0700 Subject: Solve BounceToKernel may hang issue BounceToKernel will make vCPU quit from guest ring3 to guest ring0, but vCPUWaiter is not cleared when we unlock the vCPU, when next time this vCPU enter guest mode ring3, vCPU may enter guest mode with vCPUWaiter bit setted, this will cause the following BounceToKernel to this vCPU hangs at waitUntilNot. Halt may workaroud this issue, because halt process will reset vCPU status into vCPUUser, and notify all waiter for vCPU state change, but if there is no exception or syscall in this period, BounceToKernel will hang at waitUntilNot. PiperOrigin-RevId: 256299660 --- pkg/sentry/platform/kvm/machine.go | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'pkg/sentry/platform') diff --git a/pkg/sentry/platform/kvm/machine.go b/pkg/sentry/platform/kvm/machine.go index 7d92e16cc..679087e25 100644 --- a/pkg/sentry/platform/kvm/machine.go +++ b/pkg/sentry/platform/kvm/machine.go @@ -426,7 +426,12 @@ func (c *vCPU) unlock() { // Normal state. case vCPUUser | vCPUGuest | vCPUWaiter: // Force a transition: this must trigger a notification when we - // return from guest mode. + // return from guest mode. We must clear vCPUWaiter here + // anyways, because BounceToKernel will force a transition only + // from ring3 to ring0, which will not clear this bit. Halt may + // workaround the issue, but if there is no exception or + // syscall in this period, BounceToKernel will hang. + atomicbitops.AndUint32(&c.state, ^vCPUWaiter) c.notify() case vCPUUser | vCPUWaiter: // Waiting for the lock to be released; the responsibility is -- cgit v1.2.3