virt: vmgenid: add devicetree bindings support

Changes v7->v8:
- Remove Kconfig depends statement entirely, instead of ACPI||OF.
- Check platform_get_irq() return value against < 0 rather than !0.

This is a cleanup of Sudan's OF vmgenid patches, simplified a bit, but still with the same intent and mostly unchanged. I'll take this via my random tree, but Krzysztof, I would appreciate having your ack/review on it.

Sudan - if I've mangled something here, please let me know. I verified this still works with ACPI in QEMU, but I don't know about your private firecracker OF branch, so please pipe up if something is amiss. It's basically the same thing, though, so I suspect it'll be fine.

Thanks,
Jason

Sudan Landge (3):
virt: vmgenid: change implementation to use a platform driver
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                        | 150 ++++++++++++++----
 4 files changed, 165 insertions(+), 36 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml

2.44.0

From: Sudan Landge <[email protected]>

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

---
 drivers/virt/vmgenid.c | 99 +++++++++++++++++++++++++++---------------
 1 file changed, 65 insertions(+), 34 deletions(-)

index a1c467a0e9f7..0522107f9bee 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");

@@ -21,19 +22,41 @@ struct vmgenid_state {
 	u8 this_id[VMGENID_SIZE];
 };
 
-static int vmgenid_add(struct acpi_device *device)
+static void vmgenid_notify(struct device *device)
+{
+	struct vmgenid_state *state = device->driver_data;
+	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));
+}
+
+static void setup_vmgenid_state(struct vmgenid_state *state, void *virt_addr)
 {
+	state->next_id = virt_addr;
+	memcpy(state->this_id, state->next_id, sizeof(state->this_id));
+	add_device_randomness(state->this_id, sizeof(state->this_id));
+}
+
+static void vmgenid_acpi_handler(acpi_handle __always_unused handle,
+				 u32 __always_unused event, void *dev)
+{
+	vmgenid_notify(dev);
+}
+
+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;
+	void *virt_addr;
 	int ret = 0;
 
-	state = devm_kmalloc(&device->dev, sizeof(*state), GFP_KERNEL);
-	if (!state)
-		return -ENOMEM;
-
 	status = acpi_evaluate_object(device->handle, "ADDR", NULL, &parsed);
 	if (ACPI_FAILURE(status)) {
 		ACPI_EXCEPTION((AE_INFO, status, "Evaluating ADDR"));

@@ -49,53 +72,61 @@ 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 = devm_memremap(&device->dev, phys_addr, VMGENID_SIZE, MEMREMAP_WB);
+	if (IS_ERR(virt_addr)) {
+		ret = PTR_ERR(virt_addr);
 		goto out;
 	}
+	setup_vmgenid_state(state, virt_addr);
 
-	memcpy(state->this_id, state->next_id, sizeof(state->this_id));
-	add_device_randomness(state->this_id, sizeof(state->this_id));
-
-	device->driver_data = state;
+	status = acpi_install_notify_handler(device->handle, ACPI_DEVICE_NOTIFY,
+					     vmgenid_acpi_handler, dev);
+	if (ACPI_FAILURE(status)) {
+		ret = -ENODEV;
+		goto out;
+	}
 
+	dev->driver_data = state;
 out:
 	ACPI_FREE(parsed.pointer);
 	return ret;
 }
 
-static void vmgenid_notify(struct acpi_device *device, u32 event)
+static int vmgenid_add(struct platform_device *pdev)
 {
-	struct vmgenid_state *state = acpi_driver_data(device);
-	u8 old_id[VMGENID_SIZE];
+	struct device *dev = &pdev->dev;
+	struct vmgenid_state *state;
+	int ret;
 
-	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));
+	state = devm_kmalloc(dev, sizeof(*state), GFP_KERNEL);
+	if (!state)
+		return -ENOMEM;
+
+	ret = vmgenid_add_acpi(dev, state);
+
+	if (ret < 0)
+		devm_kfree(dev, state);
+	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 },
 	{ }
 };
-
-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_DEVICE_TABLE(acpi, vmgenid_ids);
 MODULE_DESCRIPTION("Virtual Machine Generation ID");
 MODULE_LICENSE("GPL v2");
 MODULE_AUTHOR("Jason A. Donenfeld <[email protected]>");

2.44.0

From: Sudan Landge <[email protected]>

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 chose 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.

The point of vmgenid is to provide a mechanism to discover a GUID when the execution state of a virtual machine changes and the simplest way to do it is pass a memory location and an interrupt via devicetree. It would complicate things unnecessarily if instead of using devicetree, we try to implement a new protocol or modify other protocols to somehow provide the same functionility.

We believe that adding a devicetree binding for vmgenid is a simpler, better alternative to provide the same functionality and will allow such hypervisors as mentioned above to continue using devicetree.

More references to the vmgenid specs are found below.

---
 .../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 c23fda1aa1f0..efd8de759d95 100644
@@ -18469,6 +18469,7 @@ 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
 

2.44.0

From: Sudan Landge <[email protected]>

Extend the vmgenid platform driver to support devicetree bindings. With this support, hypervisors can send vmgenid notifications to the virtual machine without the need to enable ACPI. The bindings are located at:
Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml

Since this is no longer ACPI-dependent, remove the dependency from Kconfig and protect the ACPI code with a single ifdef.

[Jason: - Small style cleanups and refactoring.
- Re-work ACPI conditionalization. ]

---
 drivers/virt/Kconfig   |  1 -
 drivers/virt/vmgenid.c | 53 ++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 51 insertions(+), 3 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

2.44.0

Hi Jason,

I also verified that this still works with ACPI on Firecracker. I also verified that the OF part of the patch works with this:
https://github.com/sudanl0/firecracker/commit/f382e09a9b1e4453d2b231232d89bcb85296ac87
patch on top of Firecracker.

Cheers,
Babis

Hi Babis,

Thanks for testing this. No word from the other folks who were looking at this patchset before, so I'll move ahead and apply this to random.git and send it up for 6.10.

- [1/3] https://git.kernel.org/crng/random/c/e07606713
- [2/3] https://git.kernel.org/crng/random/c/a4aded1ff
- [3/3] https://git.kernel.org/crng/random/c/7b1bcd6b5

Jason