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authorDavid Woodhouse <dwmw@amazon.co.uk>2023-01-11 21:06:51 +0300
committerPaolo Bonzini <pbonzini@redhat.com>2023-01-12 01:45:58 +0300
commit310bc39546a435c83cc27a0eba878afac0d74714 (patch)
tree82140b99c617ba7f4c085898cb68b1aa8f40fa11 /Documentation/virt
parent42a90008f890afc41837dfeec1f0b1e7bcecf94a (diff)
downloadlinux-310bc39546a435c83cc27a0eba878afac0d74714.tar.xz
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 <dwmw@amazon.co.uk> Message-Id: <20230111180651.14394-4-dwmw2@infradead.org> [Rebase, add docs. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'Documentation/virt')
-rw-r--r--Documentation/virt/kvm/locking.rst2
1 files changed, 1 insertions, 1 deletions
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