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KVM: Don't enable hardware after a restart/shutdown is initiated 

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: 8e1c18157d ("KVM: VMX: Disable VMX when system shutdown")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Message-Id: <20230512233127.804012-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2023-05-12 16:31:27 -07:00 committed by Paolo Bonzini
parent 6735150b69
commit e0ceec221f
1 changed files with 16 additions and 1 deletions
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17
virt/kvm/kvm_main.c
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@ -5184,7 +5184,20 @@ 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()
@ -5197,6 +5210,8 @@ 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);