[PATCH 2/2] KVM: arm64: vgic-v4: Don't allocate vPEs when userspace clears nASSGIcap

[Fuad Tabba]

Since commit c652887a92887 ("KVM: arm64: vgic-v3: Allow userspace to
write GICD_TYPER2.nASSGIcap"), userspace can disable vPE allocation for
a VM on a GICv4.1 host with vSGIs by clearing nASSGIcap before the vgic
is initialised. vgic_init() then skips vgic_v4_init(), and
kvm_vgic_dist_destroy() skips vgic_v4_teardown(). vgic_its_create()
still calls vgic_v4_init() for an ITS created after the vgic is
initialised, though, and vgic_v4_init() allocates the vPEs and requests
a doorbell IRQ for each vCPU. Destroying the VM leaks them, and leaves
each doorbell handler registered with a vCPU that's about to be freed.

Rather than gate on vgic_supports_direct_irqs(), which reads has_its
before vgic_its_create() sets it, check for a cleared nASSGIcap in
vgic_v4_init().

Fixes: c652887a92887 ("KVM: arm64: vgic-v3: Allow userspace to write GICD_TYPER2.nASSGIcap")
Cc: stable at vger.kernel.org
Signed-off-by: Fuad Tabba <fuad.tabba at linux.dev>
---
 arch/arm64/kvm/vgic/vgic-v4.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c
index a01de4de608a6..12a57921f6af3 100644
--- a/arch/arm64/kvm/vgic/vgic-v4.c
+++ b/arch/arm64/kvm/vgic/vgic-v4.c
@@ -251,6 +251,10 @@ int vgic_v4_init(struct kvm *kvm)
 	if (!kvm_vgic_global_state.has_gicv4 || dist->vgic_model != KVM_DEV_TYPE_ARM_VGIC_V3)
 		return 0; /* Nothing to see here... move along. */
 
+	/* Userspace disabled vPE allocation by clearing nASSGIcap */
+	if (system_supports_direct_sgis() && !vgic_supports_direct_sgis(kvm))
+		return 0;
+
 	if (dist->its_vm.vpes)
 		return 0;
 
-- 
2.47.3