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KVM: Register /dev/kvm as the _very_ last thing during initialization

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Register /dev/kvm, i.e. expose KVM to userspace, only after all other
setup has completed.  Once /dev/kvm is exposed, userspace can start
invoking KVM ioctls, creating VMs, etc...  If userspace creates a VM
before KVM is done with its configuration, bad things may happen, e.g.
KVM will fail to properly migrate vCPU state if a VM is created before
KVM has registered preemption notifiers.

Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221130230934.1014142-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-11-30 23:08:45 +00:00 committed by Paolo Bonzini
parent fc471e8310
commit 2b01281273
1 changed files with 22 additions and 9 deletions
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31
virt/kvm/kvm_main.c
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@ -5988,12 +5988,6 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
kvm_chardev_ops.owner = module;
r = misc_register(&kvm_dev);
if (r) {
pr_err("kvm: misc device register failed\n");
goto out_unreg;
}
register_syscore_ops(&kvm_syscore_ops);
kvm_preempt_ops.sched_in = kvm_sched_in;
@ -6002,11 +5996,24 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
kvm_init_debug();
r = kvm_vfio_ops_init();
WARN_ON(r);
if (WARN_ON_ONCE(r))
goto err_vfio;
/*
* Registration _must_ be the very last thing done, as this exposes
* /dev/kvm to userspace, i.e. all infrastructure must be setup!
*/
r = misc_register(&kvm_dev);
if (r) {
pr_err("kvm: misc device register failed\n");
goto err_register;
}
return 0;
out_unreg:
err_register:
kvm_vfio_ops_exit();
err_vfio:
kvm_async_pf_deinit();
out_free_4:
for_each_possible_cpu(cpu)
@ -6032,8 +6039,14 @@ void kvm_exit(void)
{
int cpu;
debugfs_remove_recursive(kvm_debugfs_dir);
/*
* Note, unregistering /dev/kvm doesn't strictly need to come first,
* fops_get(), a.k.a. try_module_get(), prevents acquiring references
* to KVM while the module is being stopped.
*/
misc_deregister(&kvm_dev);
debugfs_remove_recursive(kvm_debugfs_dir);
for_each_possible_cpu(cpu)
free_cpumask_var(per_cpu(cpu_kick_mask, cpu));
kmem_cache_destroy(kvm_vcpu_cache);