KVM: arm64: vgic: Don't hold config_lock while unregistering redistributors

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@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Tested-by: Zenghui Yu <yuzenghui@huawei.com>
Link: https://lore.kernel.org/r/20240819125045.3474845-1-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index 41feb858ff9a5e2c83046750a8168d578e2f202a..e7c53e8af3d165379a609cbac4cc8ef2bd3be6fd 100644 (file)
--- 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 974849ea7101c6000159727a7c0077ccead78136..abe29c7d85d05a0222b2854c82d86d822480d9bb 100644 (file)
--- 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