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KVM: x86/xen: Avoid deadlock by adding kvm->arch.xen.xen_lock leaf no…
…de lock In commit 14243b3 ("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 2fd6df2 ("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: 2fd6df2 ("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]>
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