• David Woodhouse's avatar
    KVM: x86/xen: Avoid deadlock by adding kvm->arch.xen.xen_lock leaf node lock · 310bc395
    David Woodhouse authored
    In commit 14243b38 ("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 2fd6df2f ("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: 2fd6df2f ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
    Signed-off-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
    Message-Id: <20230111180651.14394-4-dwmw2@infradead.org>
    [Rebase, add docs. - Paolo]
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    310bc395
xen.c 56.9 KB