KVM: x86/xen: Avoid deadlock by adding kvm->arch.xen.xen_lock leaf node lock

In commit 14243b387137a ("KVM: x86/xen: Add KVM_IRQ_ROUTING_XEN_EVTCHN
and event channel delivery") the clever version of me left some helpful
notes for those who would come after him:

       /*
        * For the irqfd workqueue, using the main kvm->lock mutex is
        * fine since this function is invoked from kvm_set_irq() with
        * no other lock held, no srcu. In future if it will be called
        * directly from a vCPU thread (e.g. on hypercall for an IPI)
        * then it may need to switch to using a leaf-node mutex for
        * serializing the shared_info mapping.
        */
       mutex_lock(&kvm->lock);

In commit 2fd6df2f2b47 ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
the other version of me ran straight past that comment without reading it,
and introduced a potential deadlock by taking vcpu->mutex and kvm->lock
in the wrong order.

Solve this as originally suggested, by adding a leaf-node lock in the Xen
state rather than using kvm->lock for it.

Fixes: 2fd6df2f2b47 ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
Signed-off-by: David Woodhouse <[email protected]>
Message-Id: <[email protected]>
[Rebase, add docs. - Paolo]
Signed-off-by: Paolo Bonzini <[email protected]>

0 files changed, 0 insertions, 0 deletions