We recently moved the teardown of the vgic part of a vcpu inside
a critical section guarded by the config_lock. This teardown phase
involves calling into kvm_io_bus_unregister_dev(), which takes the
kvm->srcu lock.
However, this violates the established order where kvm->srcu is
taken on a memory fault (such as an MMIO access), possibly
followed by taking the config_lock if the GIC emulation requires
mutual exclusion from the other vcpus.
It therefore results in a bad lockdep splat, as reported by Zenghui.
Fix this by moving the call to kvm_io_bus_unregister_dev() outside
of the config_lock critical section. At this stage, there shouln't
be any need to hold the config_lock.
As an additional bonus, document the ordering between kvm->slots_lock,
kvm->srcu and kvm->arch.config_lock so that I cannot pretend I didn't
know about those anymore.
Fixes: 9eb18136af9f ("KVM: arm64: vgic: Hold config_lock while tearing down a CPU interface")
Reported-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
arch/arm64/kvm/vgic/vgic-init.c | 9 ++++++---
arch/arm64/kvm/vgic/vgic.c | 5 +++++
2 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index 41feb858ff9a..e7c53e8af3d1 100644
--- a/arch/arm64/kvm/vgic/vgic-init.c
+++ b/arch/arm64/kvm/vgic/vgic-init.c
@@ -417,10 +417,8 @@ static void __kvm_vgic_vcpu_destroy(struct kvm_vcpu *vcpu)
kfree(vgic_cpu->private_irqs);
vgic_cpu->private_irqs = NULL;
- if (vcpu->kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3) {
- vgic_unregister_redist_iodev(vcpu);
+ if (vcpu->kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3)
vgic_cpu->rd_iodev.base_addr = VGIC_ADDR_UNDEF;
- }
}
void kvm_vgic_vcpu_destroy(struct kvm_vcpu *vcpu)
@@ -448,6 +446,11 @@ void kvm_vgic_destroy(struct kvm *kvm)
kvm_vgic_dist_destroy(kvm);
mutex_unlock(&kvm->arch.config_lock);
+
+ if (kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3)
+ kvm_for_each_vcpu(i, vcpu, kvm)
+ vgic_unregister_redist_iodev(vcpu);
+
mutex_unlock(&kvm->slots_lock);
}
diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index 2caa64415ff3..f50274fd5581 100644
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c
@@ -36,6 +36,11 @@ struct vgic_global kvm_vgic_global_state __ro_after_init = {
* we have to disable IRQs before taking this lock and everything lower
* than it.
*
+ * The config_lock has additional ordering requirements:
+ * kvm->slots_lock
+ * kvm->srcu
+ * kvm->arch.config_lock
+ *
* If you need to take multiple locks, always take the upper lock first,
* then the lower ones, e.g. first take the its_lock, then the irq_lock.
* If you are already holding a lock and need to take a higher one, you
--
2.39.2
