From 310bc39546a435c83cc27a0eba878afac0d74714 Mon Sep 17 00:00:00 2001 From: David Woodhouse Date: Wed, 11 Jan 2023 18:06:51 +0000 Subject: 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 Message-Id: <20230111180651.14394-4-dwmw2@infradead.org> [Rebase, add docs. - Paolo] Signed-off-by: Paolo Bonzini --- Documentation/virt/kvm/locking.rst | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst index 5ee017740d55..a0146793d197 100644 --- a/Documentation/virt/kvm/locking.rst +++ b/Documentation/virt/kvm/locking.rst @@ -39,7 +39,7 @@ For SRCU: On x86: -- vcpu->mutex is taken outside kvm->arch.hyperv.hv_lock +- vcpu->mutex is taken outside kvm->arch.hyperv.hv_lock and kvm->arch.xen.xen_lock - kvm->arch.mmu_lock is an rwlock. kvm->arch.tdp_mmu_pages_lock and kvm->arch.mmu_unsync_pages_lock are taken inside kvm->arch.mmu_lock, and -- cgit v1.2.3-70-g09d2