xen/pcpu: Xen physical cpus online/offline sys interface

This patch provide Xen physical cpus online/offline sys interface.
User can use it for their own purpose, like power saving:
by offlining some cpus when light workload it save power greatly.

Its basic workflow is, user online/offline cpu via sys interface,
then hypercall xen to implement, after done xen inject virq back to dom0,
and then dom0 sync cpu status.

Signed-off-by: Jiang, Yunhong <[e-mail]>
Signed-off-by: Liu, Jinsong <[e-mail]>
Signed-off-by: Konrad Rzeszutek Wilk <[e-mail]>

Documentation/ABI/testing/sysfs-devices-system-xen_cpu

···
+What:		/sys/devices/system/xen_cpu/
+Date:		May 2012
+Contact:	Liu, Jinsong <[e-mail]>
+Description:
+		A collection of global/individual Xen physical cpu attributes
+
+		Individual physical cpu attributes are contained in
+		subdirectories named by the Xen's logical cpu number, e.g.:
+		/sys/devices/system/xen_cpu/xen_cpu#/
+
+
+What:		/sys/devices/system/xen_cpu/xen_cpu#/online
+Date:		May 2012
+Contact:	Liu, Jinsong <[e-mail]>
+Description:
+		Interface to online/offline Xen physical cpus
+
+		When running under Xen platform, it provide user interface
+		to online/offline physical cpus, except cpu0 due to several
+		logic restrictions and assumptions.

drivers/xen/Makefile

···
 obj-$(CONFIG_XEN_PVHVM)			+= platform-pci.o
 obj-$(CONFIG_XEN_TMEM)			+= tmem.o
 obj-$(CONFIG_SWIOTLB_XEN)		+= swiotlb-xen.o
+obj-$(CONFIG_XEN_DOM0)			+= pcpu.o
 obj-$(CONFIG_XEN_DOM0)			+= pci.o acpi.o
 obj-$(CONFIG_XEN_MCE_LOG)		+= mcelog.o
 obj-$(CONFIG_XEN_PCIDEV_BACKEND)	+= xen-pciback/

drivers/xen/pcpu.c

···
+/******************************************************************************
+ * pcpu.c
+ * Management physical cpu in dom0, get pcpu info and provide sys interface
+ *
+ * Copyright (c) 2012 Intel Corporation
+ * Author: Liu, Jinsong <[e-mail]>
+ * Author: Jiang, Yunhong <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <linux/interrupt.h>
+#include <linux/spinlock.h>
+#include <linux/cpu.h>
+#include <linux/stat.h>
+#include <linux/capability.h>
+
+#include <xen/xen.h>
+#include <xen/xenbus.h>
+#include <xen/events.h>
+#include <xen/interface/platform.h>
+#include <asm/xen/hypervisor.h>
+#include <asm/xen/hypercall.h>
+
+#define XEN_PCPU "xen_cpu: "
+
+/*
+ * @cpu_id: Xen physical cpu logic number
+ * @flags: Xen physical cpu status flag
+ * - XEN_PCPU_FLAGS_ONLINE: cpu is online
+ * - XEN_PCPU_FLAGS_INVALID: cpu is not present
+ */
+struct pcpu {
+	struct list_head list;
+	struct device dev;
+	uint32_t cpu_id;
+	uint32_t flags;
+};
+
+static struct bus_type xen_pcpu_subsys = {
+	.name = "xen_cpu",
+	.dev_name = "xen_cpu",
+};
+
+static DEFINE_MUTEX(xen_pcpu_lock);
+
+static LIST_HEAD(xen_pcpus);
+
+static int xen_pcpu_down(uint32_t cpu_id)
+{
+	struct xen_platform_op op = {
+		.cmd			= XENPF_cpu_offline,
+		.interface_version	= XENPF_INTERFACE_VERSION,
+		.u.cpu_ol.cpuid		= cpu_id,
+	};
+
+	return HYPERVISOR_dom0_op(&op);
+}
+
+static int xen_pcpu_up(uint32_t cpu_id)
+{
+	struct xen_platform_op op = {
+		.cmd			= XENPF_cpu_online,
+		.interface_version	= XENPF_INTERFACE_VERSION,
+		.u.cpu_ol.cpuid		= cpu_id,
+	};
+
+	return HYPERVISOR_dom0_op(&op);
+}
+
+static ssize_t show_online(struct device *dev,
+			   struct device_attribute *attr,
+			   char *buf)
+{
+	struct pcpu *cpu = container_of(dev, struct pcpu, dev);
+
+	return sprintf(buf, "%u\n", !!(cpu->flags & XEN_PCPU_FLAGS_ONLINE));
+}
+
+static ssize_t __ref store_online(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t count)
+{
+	struct pcpu *pcpu = container_of(dev, struct pcpu, dev);
+	unsigned long long val;
+	ssize_t ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (kstrtoull(buf, 0, &val) < 0)
+		return -EINVAL;
+
+	switch (val) {
+	case 0:
+		ret = xen_pcpu_down(pcpu->cpu_id);
+		break;
+	case 1:
+		ret = xen_pcpu_up(pcpu->cpu_id);
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	if (ret >= 0)
+		ret = count;
+	return ret;
+}
+static DEVICE_ATTR(online, S_IRUGO | S_IWUSR, show_online, store_online);
+
+static bool xen_pcpu_online(uint32_t flags)
+{
+	return !!(flags & XEN_PCPU_FLAGS_ONLINE);
+}
+
+static void pcpu_online_status(struct xenpf_pcpuinfo *info,
+			       struct pcpu *pcpu)
+{
+	if (xen_pcpu_online(info->flags) &&
+	   !xen_pcpu_online(pcpu->flags)) {
+		/* the pcpu is onlined */
+		pcpu->flags |= XEN_PCPU_FLAGS_ONLINE;
+		kobject_uevent(&pcpu->dev.kobj, KOBJ_ONLINE);
+	} else if (!xen_pcpu_online(info->flags) &&
+		    xen_pcpu_online(pcpu->flags)) {
+		/* The pcpu is offlined */
+		pcpu->flags &= ~XEN_PCPU_FLAGS_ONLINE;
+		kobject_uevent(&pcpu->dev.kobj, KOBJ_OFFLINE);
+	}
+}
+
+static struct pcpu *get_pcpu(uint32_t cpu_id)
+{
+	struct pcpu *pcpu;
+
+	list_for_each_entry(pcpu, &xen_pcpus, list) {
+		if (pcpu->cpu_id == cpu_id)
+			return pcpu;
+	}
+
+	return NULL;
+}
+
+static void pcpu_release(struct device *dev)
+{
+	struct pcpu *pcpu = container_of(dev, struct pcpu, dev);
+
+	list_del(&pcpu->list);
+	kfree(pcpu);
+}
+
+static void unregister_and_remove_pcpu(struct pcpu *pcpu)
+{
+	struct device *dev;
+
+	if (!pcpu)
+		return;
+
+	dev = &pcpu->dev;
+	if (dev->id)
+		device_remove_file(dev, &dev_attr_online);
+
+	/* pcpu remove would be implicitly done */
+	device_unregister(dev);
+}
+
+static int register_pcpu(struct pcpu *pcpu)
+{
+	struct device *dev;
+	int err = -EINVAL;
+
+	if (!pcpu)
+		return err;
+
+	dev = &pcpu->dev;
+	dev->bus = &xen_pcpu_subsys;
+	dev->id = pcpu->cpu_id;
+	dev->release = pcpu_release;
+
+	err = device_register(dev);
+	if (err) {
+		pcpu_release(dev);
+		return err;
+	}
+
+	/*
+	 * Xen never offline cpu0 due to several restrictions
+	 * and assumptions. This basically doesn't add a sys control
+	 * to user, one cannot attempt to offline BSP.
+	 */
+	if (dev->id) {
+		err = device_create_file(dev, &dev_attr_online);
+		if (err) {
+			device_unregister(dev);
+			return err;
+		}
+	}
+
+	return 0;
+}
+
+static struct pcpu *create_and_register_pcpu(struct xenpf_pcpuinfo *info)
+{
+	struct pcpu *pcpu;
+	int err;
+
+	if (info->flags & XEN_PCPU_FLAGS_INVALID)
+		return ERR_PTR(-ENODEV);
+
+	pcpu = kzalloc(sizeof(struct pcpu), GFP_KERNEL);
+	if (!pcpu)
+		return ERR_PTR(-ENOMEM);
+
+	INIT_LIST_HEAD(&pcpu->list);
+	pcpu->cpu_id = info->xen_cpuid;
+	pcpu->flags = info->flags;
+
+	/* Need hold on xen_pcpu_lock before pcpu list manipulations */
+	list_add_tail(&pcpu->list, &xen_pcpus);
+
+	err = register_pcpu(pcpu);
+	if (err) {
+		pr_warning(XEN_PCPU "Failed to register pcpu%u\n",
+			   info->xen_cpuid);
+		return ERR_PTR(-ENOENT);
+	}
+
+	return pcpu;
+}
+
+/*
+ * Caller should hold the xen_pcpu_lock
+ */
+static int sync_pcpu(uint32_t cpu, uint32_t *max_cpu)
+{
+	int ret;
+	struct pcpu *pcpu = NULL;
+	struct xenpf_pcpuinfo *info;
+	struct xen_platform_op op = {
+		.cmd                   = XENPF_get_cpuinfo,
+		.interface_version     = XENPF_INTERFACE_VERSION,
+		.u.pcpu_info.xen_cpuid = cpu,
+	};
+
+	ret = HYPERVISOR_dom0_op(&op);
+	if (ret)
+		return ret;
+
+	info = &op.u.pcpu_info;
+	if (max_cpu)
+		*max_cpu = info->max_present;
+
+	pcpu = get_pcpu(cpu);
+
+	/*
+	 * Only those at cpu present map has its sys interface.
+	 */
+	if (info->flags & XEN_PCPU_FLAGS_INVALID) {
+		if (pcpu)
+			unregister_and_remove_pcpu(pcpu);
+		return 0;
+	}
+
+	if (!pcpu) {
+		pcpu = create_and_register_pcpu(info);
+		if (IS_ERR_OR_NULL(pcpu))
+			return -ENODEV;
+	} else
+		pcpu_online_status(info, pcpu);
+
+	return 0;
+}
+
+/*
+ * Sync dom0's pcpu information with xen hypervisor's
+ */
+static int xen_sync_pcpus(void)
+{
+	/*
+	 * Boot cpu always have cpu_id 0 in xen
+	 */
+	uint32_t cpu = 0, max_cpu = 0;
+	int err = 0;
+	struct pcpu *pcpu, *tmp;
+
+	mutex_lock(&xen_pcpu_lock);
+
+	while (!err && (cpu <= max_cpu)) {
+		err = sync_pcpu(cpu, &max_cpu);
+		cpu++;
+	}
+
+	if (err)
+		list_for_each_entry_safe(pcpu, tmp, &xen_pcpus, list)
+			unregister_and_remove_pcpu(pcpu);
+
+	mutex_unlock(&xen_pcpu_lock);
+
+	return err;
+}
+
+static void xen_pcpu_work_fn(struct work_struct *work)
+{
+	xen_sync_pcpus();
+}
+static DECLARE_WORK(xen_pcpu_work, xen_pcpu_work_fn);
+
+static irqreturn_t xen_pcpu_interrupt(int irq, void *dev_id)
+{
+	schedule_work(&xen_pcpu_work);
+	return IRQ_HANDLED;
+}
+
+static int __init xen_pcpu_init(void)
+{
+	int irq, ret;
+
+	if (!xen_initial_domain())
+		return -ENODEV;
+
+	irq = bind_virq_to_irqhandler(VIRQ_PCPU_STATE, 0,
+				      xen_pcpu_interrupt, 0,
+				      "xen-pcpu", NULL);
+	if (irq < 0) {
+		pr_warning(XEN_PCPU "Failed to bind pcpu virq\n");
+		return irq;
+	}
+
+	ret = subsys_system_register(&xen_pcpu_subsys, NULL);
+	if (ret) {
+		pr_warning(XEN_PCPU "Failed to register pcpu subsys\n");
+		goto err1;
+	}
+
+	ret = xen_sync_pcpus();
+	if (ret) {
+		pr_warning(XEN_PCPU "Failed to sync pcpu info\n");
+		goto err2;
+	}
+
+	return 0;
+
+err2:
+	bus_unregister(&xen_pcpu_subsys);
+err1:
+	unbind_from_irqhandler(irq, NULL);
+	return ret;
+}
+arch_initcall(xen_pcpu_init);

include/xen/interface/platform.h

···
 };
 DEFINE_GUEST_HANDLE_STRUCT(xenpf_pcpuinfo);
 
+#define XENPF_cpu_online	56
+#define XENPF_cpu_offline	57
+struct xenpf_cpu_ol {
+	uint32_t cpuid;
+};
+DEFINE_GUEST_HANDLE_STRUCT(xenpf_cpu_ol);
+
 struct xen_platform_op {
 	uint32_t cmd;
 	uint32_t interface_version; /* XENPF_INTERFACE_VERSION */
···
 		struct xenpf_getidletime       getidletime;
 		struct xenpf_set_processor_pminfo set_pminfo;
 		struct xenpf_pcpuinfo          pcpu_info;
+		struct xenpf_cpu_ol            cpu_ol;
 		uint8_t                        pad[128];
 	} u;
 };

include/xen/interface/xen.h

···
 #define VIRQ_CONSOLE    2  /* (DOM0) Bytes received on emergency console. */
 #define VIRQ_DOM_EXC    3  /* (DOM0) Exceptional event for some domain.   */
 #define VIRQ_DEBUGGER   6  /* (DOM0) A domain has paused for debugging.   */
+#define VIRQ_PCPU_STATE 9  /* (DOM0) PCPU state changed                   */
 
 /* Architecture-specific VIRQ definitions. */
 #define VIRQ_ARCH_0    16