KVM: arm64: pkvm: Preserve pending SError on exit from AArch32

Don't drop a potential SError when a guest gets caught red-handed
running AArch32 code.
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://lore.kernel.org/r/20211013120346.2926621-8-maz@kernel.org

arch/arm64/kvm/hyp/nvhe/switch.c

@@ -256,7 +256,8 @@ static bool handle_aarch32_guest(struct kvm_vcpu *vcpu, u64 *exit_code)
 		 * protected VMs.
 		 */
 		vcpu->arch.target = -1;
-		*exit_code = ARM_EXCEPTION_IL;
+		*exit_code &= BIT(ARM_EXIT_WITH_SERROR_BIT);
+		*exit_code |= ARM_EXCEPTION_IL;
 		return false;
 	}