From 78a00555550042ed77b33ace7423aced228b3b4e Mon Sep 17 00:00:00 2001 From: Oliver Upton Date: Thu, 17 Oct 2024 00:19:47 +0000 Subject: [PATCH] KVM: arm64: Ensure vgic_ready() is ordered against MMIO registration kvm_vgic_map_resources() prematurely marks the distributor as 'ready', potentially allowing vCPUs to enter the guest before the distributor's MMIO registration has been made visible. Plug the race by marking the distributor as ready only after MMIO registration is completed. Rely on the implied ordering of synchronize_srcu() to ensure the MMIO registration is visible before vgic_dist::ready. This also means that writers to vgic_dist::ready are now serialized by the slots_lock, which was effectively the case already as all writers held the slots_lock in addition to the config_lock. Fixes: 59112e9c390b ("KVM: arm64: vgic: Fix a circular locking issue") Signed-off-by: Oliver Upton Link: https://lore.kernel.org/r/20241017001947.2707312-3-oliver.upton@linux.dev Signed-off-by: Marc Zyngier --- arch/arm64/kvm/vgic/vgic-init.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c index d88fdeaf6144..48c952563e85 100644 --- a/arch/arm64/kvm/vgic/vgic-init.c +++ b/arch/arm64/kvm/vgic/vgic-init.c @@ -544,14 +544,23 @@ int kvm_vgic_map_resources(struct kvm *kvm) if (ret) goto out; - dist->ready = true; dist_base = dist->vgic_dist_base; mutex_unlock(&kvm->arch.config_lock); ret = vgic_register_dist_iodev(kvm, dist_base, type); - if (ret) + if (ret) { kvm_err("Unable to register VGIC dist MMIO regions\n"); + goto out_slots; + } + /* + * kvm_io_bus_register_dev() guarantees all readers see the new MMIO + * registration before returning through synchronize_srcu(), which also + * implies a full memory barrier. As such, marking the distributor as + * 'ready' here is guaranteed to be ordered after all vCPUs having seen + * a completely configured distributor. + */ + dist->ready = true; goto out_slots; out: mutex_unlock(&kvm->arch.config_lock);