[v7,2/2] drivers/virt: vmgenid: add vm generation id driver

diff --git a/Documentation/virt/vmgenid.rst b/Documentation/virt/vmgenid.rst
new file mode 100644
index 0000000..a429c2a3
--- /dev/null
+++ b/Documentation/virt/vmgenid.rst
@@ -0,0 +1,36 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+=======
+VMGENID
+=======
+
+The VM Generation ID is a feature defined by Microsoft (paper:
+http://go.microsoft.com/fwlink/?LinkId=260709) and supported by
+multiple hypervisor vendors.
+
+The feature is required in virtualized environments by applications
+that work with local copies/caches of world-unique data such as random
+values, UUIDs, monotonically increasing counters, etc.
+Such applications can be negatively affected by VM snapshotting when
+the VM is either cloned or returned to an earlier point in time.
+
+The VM Generation ID is a simple concept through which a hypevisor
+notifies its guest that a snapshot has taken place. The vmgenid device
+provides a unique ID that changes each time the VM is restored from a
+snapshot. The hardware provided UUID value can be used to differentiate
+between VMs or different generations of the same VM.
+
+The VM Generation ID is exposed through an ACPI device by multiple
+hypervisor vendors. The driver for it lives at
+``drivers/virt/vmgenid.c``
+
+The ``vmgenid`` driver acts as a backend for the ``sysgenid`` kernel module
+(``drivers/misc/sysgenid.c``, ``Documentation/misc-devices/sysgenid.rst``)
+to drive changes to the "System Generation Id" which is further exposed
+to userspace as a monotonically increasing counter.
+
+The driver uses ACPI events to be notified by hardware of changes to the
+128-bit Vm Gen Id UUID. Since the actual UUID value is not directly exposed
+to userspace, but only used to drive the System Generation Counter, the
+driver also adds it as device randomness to improve kernel entropy
+following VM snapshot events.
diff --git a/MAINTAINERS b/MAINTAINERS
index b812dad8..f21451e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -19086,6 +19086,13 @@  F:	drivers/staging/vme/
 F:	drivers/vme/
 F:	include/linux/vme*
 
+VMGENID
+M:	Adrian Catangiu <acatan@amazon.com>
+L:	linux-kernel@vger.kernel.org
+S:	Supported
+F:	Documentation/virt/vmgenid.rst
+F:	drivers/virt/vmgenid.c
+
 VMWARE BALLOON DRIVER
 M:	Nadav Amit <namit@vmware.com>
 M:	"VMware, Inc." <pv-drivers@vmware.com>
diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig
index 80c5f9c1..95d82c9 100644
--- a/drivers/virt/Kconfig
+++ b/drivers/virt/Kconfig
@@ -13,6 +13,19 @@  menuconfig VIRT_DRIVERS
 
 if VIRT_DRIVERS
 
+config VMGENID
+	tristate "Virtual Machine Generation ID driver"
+	depends on ACPI && SYSGENID
+	help
+	  The driver uses the hypervisor provided Virtual Machine Generation ID
+	  to drive the system generation counter mechanism exposed by sysgenid.
+	  The vmgenid changes on VM snapshots or VM cloning. The hypervisor
+	  provided 128-bit vmgenid is also used as device randomness to improve
+	  kernel entropy following VM snapshot events.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called vmgenid.
+
 config FSL_HV_MANAGER
 	tristate "Freescale hypervisor management driver"
 	depends on FSL_SOC
diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile
index f28425c..889be01 100644
--- a/drivers/virt/Makefile
+++ b/drivers/virt/Makefile
@@ -4,6 +4,7 @@ 
 #
 
 obj-$(CONFIG_FSL_HV_MANAGER)	+= fsl_hypervisor.o
+obj-$(CONFIG_VMGENID)		+= vmgenid.o
 obj-y				+= vboxguest/
 
 obj-$(CONFIG_NITRO_ENCLAVES)	+= nitro_enclaves/
diff --git a/drivers/virt/vmgenid.c b/drivers/virt/vmgenid.c
new file mode 100644
index 0000000..d9d089a
--- /dev/null
+++ b/drivers/virt/vmgenid.c
@@ -0,0 +1,153 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Virtual Machine Generation ID driver
+ *
+ * Copyright (C) 2018 Red Hat Inc. All rights reserved.
+ *
+ * Copyright (C) 2020 Amazon. All rights reserved.
+ *
+ *	Authors:
+ *	  Adrian Catangiu <acatan@amazon.com>
+ *	  Or Idgar <oridgar@gmail.com>
+ *	  Gal Hammer <ghammer@redhat.com>
+ *
+ */
+#include <linux/acpi.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/random.h>
+#include <linux/uuid.h>
+#include <linux/sysgenid.h>
+
+#define DEV_NAME "vmgenid"
+ACPI_MODULE_NAME(DEV_NAME);
+
+struct vmgenid_data {
+	uuid_t uuid;
+	void *uuid_iomap;
+};
+static struct vmgenid_data vmgenid_data;
+
+static int vmgenid_acpi_map(struct vmgenid_data *priv, acpi_handle handle)
+{
+	int i;
+	phys_addr_t phys_addr;
+	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
+	acpi_status status;
+	union acpi_object *pss;
+	union acpi_object *element;
+
+	status = acpi_evaluate_object(handle, "ADDR", NULL, &buffer);
+	if (ACPI_FAILURE(status)) {
+		ACPI_EXCEPTION((AE_INFO, status, "Evaluating ADDR"));
+		return -ENODEV;
+	}
+	pss = buffer.pointer;
+	if (!pss || pss->type != ACPI_TYPE_PACKAGE || pss->package.count != 2)
+		return -EINVAL;
+
+	phys_addr = 0;
+	for (i = 0; i < pss->package.count; i++) {
+		element = &(pss->package.elements[i]);
+		if (element->type != ACPI_TYPE_INTEGER)
+			return -EINVAL;
+		phys_addr |= element->integer.value << i * 32;
+	}
+
+	priv->uuid_iomap = acpi_os_map_memory(phys_addr, sizeof(uuid_t));
+	if (!priv->uuid_iomap) {
+		pr_err("Could not map memory at 0x%llx, size %u\n",
+			   phys_addr,
+			   (u32) sizeof(uuid_t));
+		return -ENOMEM;
+	}
+
+	memcpy_fromio(&priv->uuid, priv->uuid_iomap, sizeof(uuid_t));
+
+	return 0;
+}
+
+static int vmgenid_acpi_add(struct acpi_device *device)
+{
+	int ret;
+
+	if (!device)
+		return -EINVAL;
+	device->driver_data = &vmgenid_data;
+
+	ret = vmgenid_acpi_map(device->driver_data, device->handle);
+	if (ret < 0) {
+		pr_err("vmgenid: failed to map acpi device\n");
+		device->driver_data = NULL;
+	}
+
+	return ret;
+}
+
+static int vmgenid_acpi_remove(struct acpi_device *device)
+{
+	if (!device || acpi_driver_data(device) != &vmgenid_data)
+		return -EINVAL;
+	device->driver_data = NULL;
+
+	if (vmgenid_data.uuid_iomap)
+		acpi_os_unmap_memory(vmgenid_data.uuid_iomap, sizeof(uuid_t));
+	vmgenid_data.uuid_iomap = NULL;
+
+	return 0;
+}
+
+static void vmgenid_acpi_notify(struct acpi_device *device, u32 event)
+{
+	uuid_t old_uuid;
+
+	if (!device || acpi_driver_data(device) != &vmgenid_data) {
+		pr_err("VMGENID notify with unexpected driver private data\n");
+		return;
+	}
+
+	/* update VM Generation UUID */
+	old_uuid = vmgenid_data.uuid;
+	memcpy_fromio(&vmgenid_data.uuid, vmgenid_data.uuid_iomap, sizeof(uuid_t));
+
+	if (memcmp(&old_uuid, &vmgenid_data.uuid, sizeof(uuid_t))) {
+		/* HW uuid updated */
+		sysgenid_bump_generation();
+		add_device_randomness(&vmgenid_data.uuid, sizeof(uuid_t));
+	}
+}
+
+static const struct acpi_device_id vmgenid_ids[] = {
+	{"VMGENID", 0},
+	{"QEMUVGID", 0},
+	{"", 0},
+};
+
+static struct acpi_driver acpi_vmgenid_driver = {
+	.name = "vm_generation_id",
+	.ids = vmgenid_ids,
+	.owner = THIS_MODULE,
+	.ops = {
+		.add = vmgenid_acpi_add,
+		.remove = vmgenid_acpi_remove,
+		.notify = vmgenid_acpi_notify,
+	}
+};
+
+static int __init vmgenid_init(void)
+{
+	return acpi_bus_register_driver(&acpi_vmgenid_driver);
+}
+
+static void __exit vmgenid_exit(void)
+{
+	acpi_bus_unregister_driver(&acpi_vmgenid_driver);
+}
+
+module_init(vmgenid_init);
+module_exit(vmgenid_exit);
+
+MODULE_AUTHOR("Adrian Catangiu");
+MODULE_DESCRIPTION("Virtual Machine Generation ID");
+MODULE_LICENSE("GPL");
+MODULE_VERSION("0.1");