Reject hardware enabling, i.e. VM creation, if a restart/shutdown has
been initiated to avoid re-enabling hardware between kvm_reboot() and
machine_{halt,power_off,restart}(). The restart case is especially
problematic (for x86) as enabling VMX (or clearing GIF in KVM_RUN on
SVM) blocks INIT, which results in the restart/reboot hanging as BIOS
is unable to wake and rendezvous with APs.
Note, this bug, and the original issue that motivated the addition of
kvm_reboot(), is effectively limited to a forced reboot, e.g. `reboot -f`.
In a "normal" reboot, userspace will gracefully teardown userspace before
triggering the kernel reboot (modulo bugs, errors, etc), i.e. any process
that might do ioctl(KVM_CREATE_VM) is long gone.
Fixes: 8e1c18157d87 ("KVM: VMX: Disable VMX when system shutdown")
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
virt/kvm/kvm_main.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6cdfbb2c641b..b2bf4c105181 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -5182,7 +5182,20 @@ static void hardware_disable_all(void)
static int hardware_enable_all(void)
{
atomic_t failed = ATOMIC_INIT(0);
- int r = 0;
+ int r;
+
+ /*
+ * Do not enable hardware virtualization if the system is going down.
+ * If userspace initiated a forced reboot, e.g. reboot -f, then it's
+ * possible for an in-flight KVM_CREATE_VM to trigger hardware enabling
+ * after kvm_reboot() is called. Note, this relies on system_state
+ * being set _before_ kvm_reboot(), which is why KVM uses a syscore ops
+ * hook instead of registering a dedicated reboot notifier (the latter
+ * runs before system_state is updated).
+ */
+ if (system_state == SYSTEM_HALT || system_state == SYSTEM_POWER_OFF ||
+ system_state == SYSTEM_RESTART)
+ return -EBUSY;
/*
* When onlining a CPU, cpu_online_mask is set before kvm_online_cpu()
@@ -5195,6 +5208,8 @@ static int hardware_enable_all(void)
cpus_read_lock();
mutex_lock(&kvm_lock);
+ r = 0;
+
kvm_usage_count++;
if (kvm_usage_count == 1) {
on_each_cpu(hardware_enable_nolock, &failed, 1);
--
2.40.0.rc1.284.g88254d51c5-goog
