[PATCH v2 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.

Move the part of vgic_supports_direct_msis() that doesn't depend on the
ITS into vgic_supports_vpes(), together with vgic_v4_init()'s GICv3
check. Gate vgic_v4_init() on it rather than on
vgic_supports_direct_irqs(), which reads has_its before
vgic_its_create() sets it. vgic_supports_direct_msis() returns what it
did before, since vgic_has_its() is already false for a non-GICv3 VM.

Fixes: c652887a92887 ("KVM: arm64: vgic-v3: Allow userspace to write GICD_TYPER2.nASSGIcap")
Suggested-by: Oliver Upton <oupton at kernel.org>
Cc: stable at vger.kernel.org
Signed-off-by: Fuad Tabba <fuad.tabba at linux.dev>
---
 arch/arm64/kvm/vgic/vgic-mmio-v3.c | 9 +++++++--
 arch/arm64/kvm/vgic/vgic-v4.c      | 2 +-
 arch/arm64/kvm/vgic/vgic.h         | 1 +
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
index 5913a20d83019..a60697238a7a7 100644
--- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
@@ -48,7 +48,7 @@ bool vgic_has_its(struct kvm *kvm)
 	return dist->has_its;
 }
 
-bool vgic_supports_direct_msis(struct kvm *kvm)
+bool vgic_supports_vpes(struct kvm *kvm)
 {
 	/*
 	 * Deliberately conflate vLPI and vSGI support on GICv4.1 hardware,
@@ -58,7 +58,12 @@ bool vgic_supports_direct_msis(struct kvm *kvm)
 	if (system_supports_direct_sgis() && !vgic_supports_direct_sgis(kvm))
 		return false;
 
-	return kvm_vgic_global_state.has_gicv4 && vgic_has_its(kvm);
+	return kvm_vgic_global_state.has_gicv4 && vgic_is_v3(kvm);
+}
+
+bool vgic_supports_direct_msis(struct kvm *kvm)
+{
+	return vgic_supports_vpes(kvm) && vgic_has_its(kvm);
 }
 
 bool system_supports_direct_sgis(void)
diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c
index a01de4de608a6..0a4b9a74425b4 100644
--- a/arch/arm64/kvm/vgic/vgic-v4.c
+++ b/arch/arm64/kvm/vgic/vgic-v4.c
@@ -248,7 +248,7 @@ int vgic_v4_init(struct kvm *kvm)
 
 	lockdep_assert_held(&kvm->arch.config_lock);
 
-	if (!kvm_vgic_global_state.has_gicv4 || dist->vgic_model != KVM_DEV_TYPE_ARM_VGIC_V3)
+	if (!vgic_supports_vpes(kvm))
 		return 0; /* Nothing to see here... move along. */
 
 	if (dist->its_vm.vpes)
diff --git a/arch/arm64/kvm/vgic/vgic.h b/arch/arm64/kvm/vgic/vgic.h
index b71d486ae5145..7fc29a395a7db 100644
--- a/arch/arm64/kvm/vgic/vgic.h
+++ b/arch/arm64/kvm/vgic/vgic.h
@@ -500,6 +500,7 @@ static inline bool vgic_host_has_gicv5(void)
 }
 
 bool system_supports_direct_sgis(void);
+bool vgic_supports_vpes(struct kvm *kvm);
 bool vgic_supports_direct_msis(struct kvm *kvm);
 bool vgic_supports_direct_sgis(struct kvm *kvm);
 
-- 
2.47.3