KVM: arm/arm64: Fix vgic init race

[ Upstream commit 1d47191de7e15900f8fbfe7cccd7c6e1c2d7c31a ]

The vgic_init function can race with kvm_arch_vcpu_create() which does
not hold kvm_lock() and we therefore have no synchronization primitives
to ensure we're doing the right thing.

As the user is trying to initialize or run the VM while at the same time
creating more VCPUs, we just have to refuse to initialize the VGIC in
this case rather than silently failing with a broken VCPU.

Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
index 5801261f3adddeaab819f4ffd23ecd5839d03c8a..6f7f26ae72b4505d8ef1a3fbf1606ad44fcdc16c 100644 (file)
--- a/virt/kvm/arm/vgic/vgic-init.c
+++ b/virt/kvm/arm/vgic/vgic-init.c
@@ -277,6 +277,10 @@ int vgic_init(struct kvm *kvm)
        if (vgic_initialized(kvm))
                return 0;
 
+       /* Are we also in the middle of creating a VCPU? */
+       if (kvm->created_vcpus != atomic_read(&kvm->online_vcpus))
+               return -EBUSY;
+
        /* freeze the number of spis */
        if (!dist->nr_spis)
                dist->nr_spis = VGIC_NR_IRQS_LEGACY - VGIC_NR_PRIVATE_IRQS;