hypervisor: arm64: reanimate the root cell back from the dead

We have now enough implemented functionality to return to the root
cell. We just need to enable guest traps, which will be handled by
the MMU, MMIO, and GIC code we already plugged to the port. Finally,
we restore the state of the root cell that we previously stored in
the stack.

Signed-off-by: Antonios Motakis <antonios.motakis@huawei.com>

hypervisor/arch/arm64/setup.c

@@ -31,6 +31,8 @@ int arch_init_early(void)
 int arch_cpu_init(struct per_cpu *cpu_data)
 {
 	int err = 0;
+	unsigned long hcr = HCR_VM_BIT | HCR_IMO_BIT | HCR_FMO_BIT
+				| HCR_TSC_BIT | HCR_TAC_BIT | HCR_RW_BIT;
 
 	/* switch to the permanent page tables */
 	enable_mmu_el2(hv_paging_structs.root_table);
@@ -39,6 +41,9 @@ int arch_cpu_init(struct per_cpu *cpu_data)
 	cpu_data->virt_id = cpu_data->cpu_id;
 	arm_read_sysreg(MPIDR_EL1, cpu_data->mpidr.val);
 
+	/* Setup guest traps */
+	arm_write_sysreg(HCR_EL2, hcr);
+
 	err = arch_mmu_cpu_cell_init(cpu_data);
 	if (err)
 		return err;
@@ -60,8 +65,12 @@ int arch_init_late(void)
 
 void __attribute__((noreturn)) arch_cpu_activate_vmm(struct per_cpu *cpu_data)
 {
-	trace_error(-EINVAL);
-	while (1);
+	struct registers *regs = guest_regs(cpu_data);
+
+	/* return to the caller in Linux */
+	arm_write_sysreg(ELR_EL2, regs->usr[30]);
+
+	vmreturn(regs);
 }
 
 int arch_map_device(void *paddr, void *vaddr, unsigned long size)