xen/riscv: Implement construct_domain()

Implement construct_domain() function for RISC-V, which performs initial setup
for the domain's first vCPU, loads the kernel, initrd, and device tree,
and sets up guest CPU registers for boot.

It also creates additional vCPUs up to max_vcpus and assigns the device tree
address and boot cpuid in registers.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/riscv/Makefile

@@ -1,6 +1,7 @@
 obj-y += aplic.o
 obj-y += cpufeature.o
 obj-y += domain.o
+obj-y += domain-build.init.o
 obj-$(CONFIG_DOM0LESS_BOOT) += dom0less-build.init.o
 obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
 obj-y += entry.o

xen/arch/riscv/domain-build.c

@@ -0,0 +1,50 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include <xen/fdt-domain-build.h>
+#include <xen/fdt-kernel.h>
+#include <xen/init.h>
+#include <xen/sched.h>
+
+#include <asm/current.h>
+#include <asm/guest_access.h>
+
+int __init construct_domain(struct domain *d, struct kernel_info *kinfo)
+{
+    struct vcpu *v = d->vcpu[0];
+    struct cpu_user_regs *regs = vcpu_guest_cpu_user_regs(v);
+
+    BUG_ON(v->is_initialised);
+
+    /*
+     * At the moment *_load() don't return value and will just panic()
+     * inside.
+     * TODO: it will be good to change that.
+     */
+    kernel_load(kinfo);
+    initrd_load(kinfo, copy_to_guest_phys);
+    dtb_load(kinfo, copy_to_guest_phys);
+
+    regs->sepc = kinfo->entry;
+
+    /* Guest boot cpuid = 0 */
+    regs->a0 = 0;
+    regs->a1 = kinfo->dtb_paddr;
+
+    for ( unsigned int i = 1; i < d->max_vcpus; i++ )
+    {
+        const struct vcpu *tmp_v = vcpu_create(d, i);
+
+        if ( !tmp_v )
+        {
+            printk("Failed to allocate %pdv%u\n", d, i);
+            break;
+        }
+    }
+
+    domain_update_node_affinity(d);
+
+    v->is_initialised = true;
+    clear_bit(_VPF_down, &v->pause_flags);
+
+    return 0;
+}