[PATCH v2 1/2] KVM: Start populating /sys/hypervisor with KVM entries

[Filippo Sironi <sironi@amazon.de>]

Start populating /sys/hypervisor with KVM entries when we're running on
KVM. This is to replicate functionality that's available when we're
running on Xen.

Start with /sys/hypervisor/uuid, which users prefer over
/sys/devices/virtual/dmi/id/product_uuid as a way to recognize a virtual
machine, since it's also available when running on Xen HVM and on Xen PV
and, on top of that doesn't require root privileges by default.
Let's create arch-specific hooks so that different architectures can
provide different implementations.

Signed-off-by: Filippo Sironi <sironi@amazon.de>
---
v2:
* move the retrieval of the VM UUID out of uuid_show and into
  kvm_para_get_uuid, which is a weak function that can be overwritten

 drivers/Kconfig              |  2 ++
 drivers/Makefile             |  2 ++
 drivers/kvm/Kconfig          | 14 ++++++++++++++
 drivers/kvm/Makefile         |  1 +
 drivers/kvm/sys-hypervisor.c | 30 ++++++++++++++++++++++++++++++
 5 files changed, 49 insertions(+)
 create mode 100644 drivers/kvm/Kconfig
 create mode 100644 drivers/kvm/Makefile
 create mode 100644 drivers/kvm/sys-hypervisor.c

diff --git a/drivers/Kconfig b/drivers/Kconfig
index 45f9decb9848..90eb835fe951 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -146,6 +146,8 @@ source "drivers/hv/Kconfig"
 
 source "drivers/xen/Kconfig"
 
+source "drivers/kvm/Kconfig"
+
 source "drivers/staging/Kconfig"
 
 source "drivers/platform/Kconfig"
diff --git a/drivers/Makefile b/drivers/Makefile
index c61cde554340..79cc92a3f6bf 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -44,6 +44,8 @@ obj-y				+= soc/
 obj-$(CONFIG_VIRTIO)		+= virtio/
 obj-$(CONFIG_XEN)		+= xen/
 
+obj-$(CONFIG_KVM_GUEST)		+= kvm/
+
 # regulators early, since some subsystems rely on them to initialize
 obj-$(CONFIG_REGULATOR)		+= regulator/
 
diff --git a/drivers/kvm/Kconfig b/drivers/kvm/Kconfig
new file mode 100644
index 000000000000..3fc041df7c11
--- /dev/null
+++ b/drivers/kvm/Kconfig
@@ -0,0 +1,14 @@
+menu "KVM driver support"
+        depends on KVM_GUEST
+
+config KVM_SYS_HYPERVISOR
+        bool "Create KVM entries under /sys/hypervisor"
+        depends on SYSFS
+        select SYS_HYPERVISOR
+        default y
+        help
+          Create KVM entries under /sys/hypervisor (e.g., uuid). When running
+          native or on another hypervisor, /sys/hypervisor may still be
+          present, but it will have no KVM entries.
+
+endmenu
diff --git a/drivers/kvm/Makefile b/drivers/kvm/Makefile
new file mode 100644
index 000000000000..73a43fc994b9
--- /dev/null
+++ b/drivers/kvm/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_KVM_SYS_HYPERVISOR) += sys-hypervisor.o
diff --git a/drivers/kvm/sys-hypervisor.c b/drivers/kvm/sys-hypervisor.c
new file mode 100644
index 000000000000..43b1d1a09807
--- /dev/null
+++ b/drivers/kvm/sys-hypervisor.c
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <asm/kvm_para.h>
+
+#include <linux/kobject.h>
+#include <linux/sysfs.h>
+
+__weak const char *kvm_para_get_uuid(void)
+{
+	return NULL;
+}
+
+static ssize_t uuid_show(struct kobject *obj,
+			 struct kobj_attribute *attr,
+			 char *buf)
+{
+	const char *uuid = kvm_para_get_uuid();
+	return sprintf(buf, "%s\n", uuid);
+}
+
+static struct kobj_attribute uuid = __ATTR_RO(uuid);
+
+static int __init uuid_init(void)
+{
+	if (!kvm_para_available())
+		return 0;
+	return sysfs_create_file(hypervisor_kobj, &uuid.attr);
+}
+
+device_initcall(uuid_init);
-- 
2.7.4


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