KVM: arm64: vgic-v3: Consistently populate ID_AA64PFR0_EL1.GIC

When adding support for the slightly wonky Apple M1, we had to
populate ID_AA64PFR0_EL1.GIC==1 to present something to the guest,
as the HW itself doesn't advertise the feature.

However, we gated this on the in-kernel irqchip being created.
This causes some trouble for QEMU, which snapshots the state of
the registers before creating a virtual GIC, and then tries to
restore these registers once the GIC has been created.  Obviously,
between the two stages, ID_AA64PFR0_EL1.GIC has changed value,
and the write fails.

The fix is to actually emulate the HW, and always populate the
field if the HW is capable of it.

Fixes: 562e530 ("KVM: arm64: Force ID_AA64PFR0_EL1.GIC=1 when exposing a virtual GICv3")
Cc: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Oliver Upton <oupton@google.com>
Link: https://lore.kernel.org/r/20220503211424.3375263-1-maz@kernel.org

arch/arm64/kvm/sys_regs.c

@@ -1123,8 +1123,7 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 		val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_CSV2), (u64)vcpu->kvm->arch.pfr0_csv2);
 		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR0_CSV3);
 		val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_CSV3), (u64)vcpu->kvm->arch.pfr0_csv3);
-		if (irqchip_in_kernel(vcpu->kvm) &&
-		    vcpu->kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3) {
+		if (kvm_vgic_global_state.type == VGIC_V3) {
 			val &= ~ARM64_FEATURE_MASK(ID_AA64PFR0_GIC);
 			val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_GIC), 1);
 		}