virt: vmgenid: Add devicetree bindings support

This small series of patches aims to add devicetree bindings support for the Virtual Machine Generation ID (vmgenid).

Virtual Machine Generation ID was introduced in commit af6b54e2b5ba ("virt: vmgenid: notify RNG of VM fork and supply generation ID") as an ACPI only device.

VMGenID specification http://go.microsoft.com/fwlink/?LinkId=260709 defines a mechanism for the BIOS/hypervisors to communicate to the virtual machine that it is executed with a different configuration (e.g. snapshot execution or creation from a template).
The guest operating system can use the notification for various purposes such as re-initializing its random number generator etc.

More references to vmgenid specs:
- https://www.qemu.org/docs/master/specs/vmgenid.html
- https://learn.microsoft.com/en-us/windows/win32/hyperv_v2/
virtual-machine-generation-identifier

*Reason for this change*:
Chosing ACPI or devicetree is an intrinsic part of an hypervisor design. Without going into details of why a hypervisor would choose DT over ACPI, we would like to highlight that the hypervisors that have chosen devicetree and now want to make use of the vmgenid functionality cannot do so today because vmgenid is an ACPI only device.
This forces these hypervisors to change their design which could have undesirable impacts on their use-cases, test-scenarios etc.

vmgenid exposes to the guest a 16-byte cryptographically random number, the value of which changes every time it starts executing from a new configuration (snapshot, backup, etc.). During initialization, the device exposes to the guest the address of the generation ID and
an interrupt number, which the device will use to notify the guest when the generation ID changes.
These attributes can be trivially communicated via device tree bindings.

We believe that adding a devicetree binding for vmgenid is a simpler alternative way to expose the device to the guest than forcing the hypervisors to implement ACPI.

Addtional notes:
While adding the devicetree support we considered re-using existing structures/code to avoid duplicating code and reduce maintenance; so, we used the same driver to be configured either by ACPI or by DT. This also meant reimplementing the existing vmgenid ACPI bus driver as a platform driver and making it discoverable using driver.of_match_table and driver.acpi_match_table.

There is no user impact or change in vmgenid functionality when used with ACPI. We verified ACPI support of these patches on X86 and DT support on ARM using Firecracker hypervisor
https://github.com/firecracker-microvm/firecracker.

To check schema and syntax errors, the bindings file is verified with:

```
  make dt_binding_check \
  DT_SCHEMA_FILES=\
  Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml
```

and the patches were verified with:
scripts/checkpatch.pl --strict v4-000*.

Changelog with respect to version 3:
- Changed the compatible string from "virtual,vmgenctr" to "microsoft,vmgenid" as per review comments.
- Renamed vmgenid.yaml to follow DT file naming convention.
- Updated the description of properties and example in vmgenid yaml file.
- Addressed the review comments to remove all ifdefs in vmgenid.c with one exception which still needs to be under CONFIG_ACPI.
- reformated the code with clang-format.
- Tested code with W=1, Sparse, Smatch and Coccinelle tools.

Changelog with respect to version 2:
- As per review comments, used platform apis instead of "of_*" APIs, removed unnecessary #include and used IF_ENABLED instead of ifdef.
- Added more info for vmgenid buffer address and corrected the formatting.
- Replaced the compatible string from "linux,*" to "virtual,*" because, the device does not have a vendor.

Changelog with respect to version 1:
- Moved vmgenid.yaml bindings to the more related "rng" folder.
- Removed vmgenid_remove to since it is unrelated to the current goal of the patch.
- Updated the cover letter and bindings commit "[PATCH v2 3/4] dt-bindings: rng: Add vmgenid support" to provide more information on vmgenid.
- Compiled with and without CONFIG_OF/CONFIG_ACPI and fixed compilers errors/warnings.

Sudan Landge (5):
virt: vmgenid: rearrange code to make review easier
virt: vmgenid: change implementation to use a platform driver
virt: vmgenid: enable driver regardless of ACPI config
dt-bindings: rng: Add vmgenid support
virt: vmgenid: add support for devicetree bindings

 .../bindings/rng/microsoft,vmgenid.yaml       |  49 +++++
 MAINTAINERS                                   |   1 +
 drivers/virt/Kconfig                          |   1 -
 drivers/virt/vmgenid.c                        | 168 ++++++++++++++----
 4 files changed, 180 insertions(+), 39 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml

base-commit: 20cb38a7af88dc40095da7c2c9094da3873fea23

2.34.1

Rearrage the functions of vmgenid to make the next commit, which re-implements vmgenid as a platform driver, easier to review.

---
 drivers/virt/vmgenid.c | 30 +++++++++++++++---------------
 1 file changed, 15 insertions(+), 15 deletions(-)

index b67a28da4702..a167ccfad299 100644
@@ -21,6 +21,20 @@ struct vmgenid_state {
 	u8 this_id[VMGENID_SIZE];
 };
 
+static void vmgenid_notify(struct acpi_device *device, u32 event)
+{
+	struct vmgenid_state *state = acpi_driver_data(device);
+	char *envp[] = { "NEW_VMGENID=1", NULL };
+	u8 old_id[VMGENID_SIZE];
+
+	memcpy(old_id, state->this_id, sizeof(old_id));
+	memcpy(state->this_id, state->next_id, sizeof(state->this_id));
+	if (!memcmp(old_id, state->this_id, sizeof(old_id)))
+		return;
+	add_vmfork_randomness(state->this_id, sizeof(state->this_id));
+	kobject_uevent_env(&device->dev.kobj, KOBJ_CHANGE, envp);
+}
+
 static int vmgenid_add(struct acpi_device *device)
 {
 	struct acpi_buffer parsed = { ACPI_ALLOCATE_BUFFER };

@@ -65,25 +79,12 @@ static int vmgenid_add(struct acpi_device *device)
 	return ret;
 }
 
-static void vmgenid_notify(struct acpi_device *device, u32 event)
-{
-	struct vmgenid_state *state = acpi_driver_data(device);
-	char *envp[] = { "NEW_VMGENID=1", NULL };
-	u8 old_id[VMGENID_SIZE];
-
-	memcpy(old_id, state->this_id, sizeof(old_id));
-	memcpy(state->this_id, state->next_id, sizeof(state->this_id));
-	if (!memcmp(old_id, state->this_id, sizeof(old_id)))
-		return;
-	add_vmfork_randomness(state->this_id, sizeof(state->this_id));
-	kobject_uevent_env(&device->dev.kobj, KOBJ_CHANGE, envp);
-}
-
 static const struct acpi_device_id vmgenid_ids[] = {
 	{ "VMGENCTR", 0 },
 	{ "VM_GEN_COUNTER", 0 },
 	{ }
 };
+MODULE_DEVICE_TABLE(acpi, vmgenid_ids);
 
 static struct acpi_driver vmgenid_driver = {
 	.name = "vmgenid",

@@ -97,7 +98,6 @@ static struct acpi_driver vmgenid_driver = {
 
 module_acpi_driver(vmgenid_driver);
 
-MODULE_DEVICE_TABLE(acpi, vmgenid_ids);
 MODULE_DESCRIPTION("Virtual Machine Generation ID");
 MODULE_LICENSE("GPL v2");
 MODULE_AUTHOR("Jason A. Donenfeld <[email protected]>");

2.34.1

Re-implement vmgenid as a platform driver in preparation for adding devicetree bindings support in next commits.

---
 drivers/virt/vmgenid.c | 97 +++++++++++++++++++++++++++++-------------
 1 file changed, 67 insertions(+), 30 deletions(-)

index a167ccfad299..c028e2064fdd 100644
@@ -7,9 +7,10 @@
  * information to random.c.
  */
 
+#include <linux/acpi.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
-#include <linux/acpi.h>
+#include <linux/platform_device.h>
 #include <linux/random.h>
 
 ACPI_MODULE_NAME("vmgenid");

@@ -21,9 +22,9 @@ struct vmgenid_state {
 	u8 this_id[VMGENID_SIZE];
 };
 
-static void vmgenid_notify(struct acpi_device *device, u32 event)
+static void vmgenid_notify(struct device *device)
 {
-	struct vmgenid_state *state = acpi_driver_data(device);
+	struct vmgenid_state *state = device->driver_data;
 	char *envp[] = { "NEW_VMGENID=1", NULL };
 	u8 old_id[VMGENID_SIZE];
 

@@ -32,21 +33,36 @@ static void vmgenid_notify(struct acpi_device *device, u32 event)
 	if (!memcmp(old_id, state->this_id, sizeof(old_id)))
 		return;
 	add_vmfork_randomness(state->this_id, sizeof(state->this_id));
-	kobject_uevent_env(&device->dev.kobj, KOBJ_CHANGE, envp);
+	kobject_uevent_env(&device->kobj, KOBJ_CHANGE, envp);
+}
+
+static void vmgenid_acpi_handler(acpi_handle __always_unused handle,
+				 u32 __always_unused event, void *dev)
+{
+	vmgenid_notify(dev);
+}
+
+static int setup_vmgenid_state(struct vmgenid_state *state, u8 *next_id)
+{
+	if (IS_ERR(next_id))
+		return PTR_ERR(next_id);
+
+	state->next_id = next_id;
+	memcpy(state->this_id, state->next_id, sizeof(state->this_id));
+	add_device_randomness(state->this_id, sizeof(state->this_id));
+	return 0;
 }
 
-static int vmgenid_add(struct acpi_device *device)
+static int vmgenid_add_acpi(struct device *dev,
+			    struct vmgenid_state *state)
 {
+	struct acpi_device *device = ACPI_COMPANION(dev);
 	struct acpi_buffer parsed = { ACPI_ALLOCATE_BUFFER };
-	struct vmgenid_state *state;
 	union acpi_object *obj;
 	phys_addr_t phys_addr;
 	acpi_status status;
 	int ret = 0;
-
-	state = devm_kmalloc(&device->dev, sizeof(*state), GFP_KERNEL);
-	if (!state)
-		return -ENOMEM;
+	u8 *virt_addr;
 
 	status = acpi_evaluate_object(device->handle, "ADDR", NULL, &parsed);
 	if (ACPI_FAILURE(status)) {

@@ -63,40 +79,61 @@ static int vmgenid_add(struct acpi_device *device)
 
 	phys_addr = (obj->package.elements[0].integer.value << 0) |
 		    (obj->package.elements[1].integer.value << 32);
-	state->next_id = devm_memremap(&device->dev, phys_addr, VMGENID_SIZE, MEMREMAP_WB);
-	if (IS_ERR(state->next_id)) {
-		ret = PTR_ERR(state->next_id);
+
+	virt_addr = (u8 *)devm_memremap(&device->dev, phys_addr,
+					VMGENID_SIZE, MEMREMAP_WB);
+	ret = setup_vmgenid_state(state, virt_addr);
+	if (ret)
+		goto out;
+
+	dev->driver_data = state;
+	status = acpi_install_notify_handler(device->handle, ACPI_DEVICE_NOTIFY,
+					     vmgenid_acpi_handler, dev);
+	if (ACPI_FAILURE(status)) {
+		dev_err(dev, "Failed to install acpi notify handler");
+		ret = -ENODEV;
+		dev->driver_data = NULL;
 		goto out;
 	}
+out:
+	ACPI_FREE(parsed.pointer);
+	return ret;
+}
 
-	memcpy(state->this_id, state->next_id, sizeof(state->this_id));
-	add_device_randomness(state->this_id, sizeof(state->this_id));
+static int vmgenid_add(struct platform_device *pdev)
+{
+	struct vmgenid_state *state;
+	struct device *dev = &pdev->dev;
+	int ret = 0;
 
-	device->driver_data = state;
+	state = devm_kmalloc(dev, sizeof(*state), GFP_KERNEL);
+	if (!state)
+		return -ENOMEM;
+
+	ret = vmgenid_add_acpi(dev, state);
+
+	if (ret)
+		devm_kfree(dev, state);
 
-out:
-	ACPI_FREE(parsed.pointer);
 	return ret;
 }
 
-static const struct acpi_device_id vmgenid_ids[] = {
+static const struct acpi_device_id vmgenid_acpi_ids[] = {
 	{ "VMGENCTR", 0 },
 	{ "VM_GEN_COUNTER", 0 },
 	{ }
 };
-MODULE_DEVICE_TABLE(acpi, vmgenid_ids);
-
-static struct acpi_driver vmgenid_driver = {
-	.name = "vmgenid",
-	.ids = vmgenid_ids,
-	.owner = THIS_MODULE,
-	.ops = {
-		.add = vmgenid_add,
-		.notify = vmgenid_notify
-	}
+MODULE_DEVICE_TABLE(acpi, vmgenid_acpi_ids);
+
+static struct platform_driver vmgenid_plaform_driver = {
+	.probe      = vmgenid_add,
+	.driver     = {
+		.name   = "vmgenid",
+		.acpi_match_table = vmgenid_acpi_ids,
+	},
 };
 
-module_acpi_driver(vmgenid_driver);
+module_platform_driver(vmgenid_plaform_driver)
 
 MODULE_DESCRIPTION("Virtual Machine Generation ID");
 MODULE_LICENSE("GPL v2");

2.34.1

Since with next commits vmgenid driver will support both ACPI and devicetree, and since either one of CONFIG_ACPI or CONFIG_OF will always be enabled, there is no need for the driver compilation to depend on ACPI/OF. So, remove ACPI dependency for compiling the driver.

---
 drivers/virt/Kconfig   |  1 -
 drivers/virt/vmgenid.c | 16 +++++++++++-----
 2 files changed, 11 insertions(+), 6 deletions(-)

index 40129b6f0eca..d8c848cf09a6 100644
@@ -16,7 +16,6 @@ if VIRT_DRIVERS
 config VMGENID
 	tristate "Virtual Machine Generation ID driver"
 	default y
-	depends on ACPI
 	help
 	  Say Y here to use the hypervisor-provided Virtual Machine Generation ID
 	  to reseed the RNG when the VM is cloned. This is highly recommended if

index c028e2064fdd..3d93e3fb94c4 100644
@@ -36,13 +36,15 @@ static void vmgenid_notify(struct device *device)
 	kobject_uevent_env(&device->kobj, KOBJ_CHANGE, envp);
 }
 
-static void vmgenid_acpi_handler(acpi_handle __always_unused handle,
-				 u32 __always_unused event, void *dev)
+static void __maybe_unused
+vmgenid_acpi_handler(acpi_handle __always_unused handle,
+		     u32 __always_unused event, void *dev)
 {
 	vmgenid_notify(dev);
 }
 
-static int setup_vmgenid_state(struct vmgenid_state *state, u8 *next_id)
+static int __maybe_unused
+setup_vmgenid_state(struct vmgenid_state *state, u8 *next_id)
 {
 	if (IS_ERR(next_id))
 		return PTR_ERR(next_id);

@@ -53,9 +55,10 @@ static int setup_vmgenid_state(struct vmgenid_state *state, u8 *next_id)
 	return 0;
 }
 
-static int vmgenid_add_acpi(struct device *dev,
-			    struct vmgenid_state *state)
+static int vmgenid_add_acpi(struct device __maybe_unused *dev,
+			    struct vmgenid_state __maybe_unused *state)
 {
+#if IS_ENABLED(CONFIG_ACPI)
 	struct acpi_device *device = ACPI_COMPANION(dev);
 	struct acpi_buffer parsed = { ACPI_ALLOCATE_BUFFER };
 	union acpi_object *obj;

@@ -98,6 +101,9 @@ static int vmgenid_add_acpi(struct device *dev,
 out:
 	ACPI_FREE(parsed.pointer);
 	return ret;
+#else
+	return -EINVAL;
+#endif
 }
 
 static int vmgenid_add(struct platform_device *pdev)

2.34.1

Virtual Machine Generation ID driver was introduced in commit af6b54e2b5ba ("virt: vmgenid: notify RNG of VM fork and supply generation ID"), as an ACPI only device.

VMGenID specification http://go.microsoft.com/fwlink/?LinkId=260709 defines a mechanism for the BIOS/hypervisors to communicate to the virtual machine that it is executed with a different configuration (e.g. snapshot execution or creation from a template).
The guest operating system can use the notification for various purposes such as re-initializing its random number generator etc.

As per the specs, hypervisor should provide a globally unique identified, or GUID via ACPI.

This patch tries to mimic the mechanism to provide the same functionality which is for a hypervisor/BIOS to notify the virtual machine when it is executed with a different configuration.

As part of this support the devicetree bindings requires the hypervisors or BIOS to provide a memory address which holds the GUID and an IRQ which is used to notify when there is a change in the GUID.
The memory exposed in the DT should follow the rules defined in the vmgenid spec mentioned above.

*Reason for this change*:
Chosing ACPI or devicetree is an intrinsic part of an hypervisor design. Without going into details of why a hypervisor would choose DT over ACPI, we would like to highlight that the hypervisors that have chose devicetree and now want to make use of the vmgenid functionality cannot do so today because vmgenid is an ACPI only device.
This forces these hypervisors to change their design which could have undesirable impacts on their use-cases, test-scenarios etc.

vmgenid exposes to the guest a 16-byte cryptographically random number, the value of which changes every time it starts executing from a new configuration (snapshot, backup, etc.). During initialization, the device exposes to the guest the address of the generation ID and
an interrupt number, which the device will use to notify the guest when the generation ID changes.
These attributes can be trivially communicated via device tree bindings.

We believe that adding a devicetree binding for vmgenid is a simpler alternative way to expose the device to the guest than forcing the hypervisors to implement ACPI.

More references to vmgenid specs:
- https://www.qemu.org/docs/master/specs/vmgenid.html
- https://learn.microsoft.com/en-us/windows/win32/hyperv_v2/virtual-
machine-generation-identifier

---
 .../bindings/rng/microsoft,vmgenid.yaml       | 49 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 2 files changed, 50 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml

new file mode 100644
index 000000000000..8f20dee93e7e
@@ -0,0 +1,49 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/rng/microsoft,vmgenid.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Virtual Machine Generation ID
+
+maintainers:
+  - Jason A. Donenfeld <[email protected]>
+
+description:
+  Firmwares or hypervisors can use this devicetree to describe an
+  interrupt and a shared resource to inject a Virtual Machine Generation ID.
+  Virtual Machine Generation ID is a globally unique identifier (GUID) and
+  the devicetree binding follows VMGenID specification defined in
+  http://go.microsoft.com/fwlink/?LinkId=260709.
+
+properties:
+  compatible:
+    const: microsoft,vmgenid
+
+  reg:
+    description:
+      Specifies a 16-byte VMGenID in endianness-agnostic hexadecimal format.
+    maxItems: 1
+
+  interrupts:
+    description:
+      Interrupt used to notify that a new VMGenID is available.
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - interrupts
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    rng@80000000 {
+      compatible = "microsoft,vmgenid";
+      reg = <0x80000000 0x1000>;
+      interrupts = <GIC_SPI 35 IRQ_TYPE_EDGE_RISING>;
+    };
+
+...

index aea47e04c3a5..243607744b7e 100644
@@ -18476,6 +18476,7 @@ M:	"Theodore Ts'o" <[email protected]>
 M:	Jason A. Donenfeld <[email protected]>
 S:	Maintained
 T:	git https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git
+F:	Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml
 F:	drivers/char/random.c
 F:	drivers/virt/vmgenid.c
 

2.34.1

Due to a mail server error the last patch of this series, "Re: [PATCH v4 5/5] virt: vmgenid: add support for devicetree bindings", got sent separately. Apologies for this. I will resend the patches to correct this issue so, I request reviewers to please ignore this patch.