KVM: arm/arm64: Fix vgic init race

BugLink: https://bugs.launchpad.net/bugs/1836117
[ 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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
index 743ca5cb05ef6ec4a2e16ab09802aaa760fff219..094b781f5a468579494bfd60c35c66b063f8e0a7 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;