KVM: fix OOPS on flush_work

The conversion done by commit 3706feacd007 ("KVM: Remove deprecated
create_singlethread_workqueue") is broken.  It flushes a single work
item &irqfd->shutdown instead of all of them, and even worse if there
is no irqfd on the list then you get a NULL pointer dereference.
Revert the virt/kvm/eventfd.c part of that patch; to avoid the
deprecated function, just allocate our own workqueue---it does
not even have to be unbound---with alloc_workqueue.

Fixes: 3706feacd007
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 28510e72618a0..d92c3d5b0fbe6 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3846,7 +3846,12 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
 	 * kvm_arch_init makes sure there's at most one caller
 	 * for architectures that support multiple implementations,
 	 * like intel and amd on x86.
+	 * kvm_arch_init must be called before kvm_irqfd_init to avoid creating
+	 * conflicts in case kvm is already setup for another implementation.
 	 */
+	r = kvm_irqfd_init();
+	if (r)
+		goto out_irqfd;
 
 	if (!zalloc_cpumask_var(&cpus_hardware_enabled, GFP_KERNEL)) {
 		r = -ENOMEM;
@@ -3928,6 +3933,7 @@ out_free_0a:
 	free_cpumask_var(cpus_hardware_enabled);
 out_free_0:
 	kvm_irqfd_exit();
+out_irqfd:
 	kvm_arch_exit();
 out_fail:
 	return r;