virt: acrn: Introduce an interface for Service VM to control vCPU

ACRN supports partition mode to achieve real-time requirements. In
partition mode, a CPU core can be dedicated to a vCPU of User VM. The
local APIC of the dedicated CPU core can be passthrough to the User VM.
The Service VM controls the assignment of the CPU cores.

Introduce an interface for the Service VM to remove the control of CPU
core from hypervisor perspective so that the CPU core can be a dedicated
CPU core of User VM.

Cc: Zhi Wang <[e-mail]>
Cc: Zhenyu Wang <[e-mail]>
Cc: Yu Wang <[e-mail]>
Cc: Reinette Chatre <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Reviewed-by: Zhi Wang <[e-mail]>
Reviewed-by: Reinette Chatre <[e-mail]>
Signed-off-by: Shuo Liu <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/virt/acrn/hsm.c

···
  *	Yakui Zhao <[e-mail]>
  */
 
+#include <linux/cpu.h>
 #include <linux/io.h>
 #include <linux/mm.h>
 #include <linux/module.h>
···
 	return 0;
 }
 
+static ssize_t remove_cpu_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	u64 cpu, lapicid;
+	int ret;
+
+	if (kstrtoull(buf, 0, &cpu) < 0)
+		return -EINVAL;
+
+	if (cpu >= num_possible_cpus() || cpu == 0 || !cpu_is_hotpluggable(cpu))
+		return -EINVAL;
+
+	if (cpu_online(cpu))
+		remove_cpu(cpu);
+
+	lapicid = cpu_data(cpu).apicid;
+	dev_dbg(dev, "Try to remove cpu %lld with lapicid %lld\n", cpu, lapicid);
+	ret = hcall_sos_remove_cpu(lapicid);
+	if (ret < 0) {
+		dev_err(dev, "Failed to remove cpu %lld!\n", cpu);
+		goto fail_remove;
+	}
+
+	return count;
+
+fail_remove:
+	add_cpu(cpu);
+	return ret;
+}
+static DEVICE_ATTR_WO(remove_cpu);
+
+static struct attribute *acrn_attrs[] = {
+	&dev_attr_remove_cpu.attr,
+	NULL
+};
+
+static struct attribute_group acrn_attr_group = {
+	.attrs = acrn_attrs,
+};
+
+static const struct attribute_group *acrn_attr_groups[] = {
+	&acrn_attr_group,
+	NULL
+};
+
 static const struct file_operations acrn_fops = {
 	.owner		= THIS_MODULE,
 	.open		= acrn_dev_open,
···
 	.minor	= MISC_DYNAMIC_MINOR,
 	.name	= "acrn_hsm",
 	.fops	= &acrn_fops,
+	.groups	= acrn_attr_groups,
 };
 
 static int __init hsm_init(void)

drivers/virt/acrn/hypercall.h

···
 
 #define HC_ID 0x80UL
 
+#define HC_ID_GEN_BASE			0x0UL
+#define HC_SOS_REMOVE_CPU		_HC_ID(HC_ID, HC_ID_GEN_BASE + 0x01)
+
 #define HC_ID_VM_BASE			0x10UL
 #define HC_CREATE_VM			_HC_ID(HC_ID, HC_ID_VM_BASE + 0x00)
 #define HC_DESTROY_VM			_HC_ID(HC_ID, HC_ID_VM_BASE + 0x01)
···
 
 #define HC_ID_PM_BASE			0x80UL
 #define HC_PM_GET_CPU_STATE		_HC_ID(HC_ID, HC_ID_PM_BASE + 0x00)
+
+/**
+ * hcall_sos_remove_cpu() - Remove a vCPU of Service VM
+ * @cpu: The vCPU to be removed
+ *
+ * Return: 0 on success, <0 on failure
+ */
+static inline long hcall_sos_remove_cpu(u64 cpu)
+{
+	return acrn_hypercall1(HC_SOS_REMOVE_CPU, cpu);
+}
 
 /**
  * hcall_create_vm() - Create a User VM