[PATCH v8 0/3] virt: vmgenid: add devicetree bindings support

[PATCH v8 0/3] virt: vmgenid: add devicetree bindings support

[Jason A. Donenfeld]

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

[PATCH v8 1/3] virt: vmgenid: change implementation to use a platform driver

[Jason A. Donenfeld]

From: Sudan Landge <sudanl@amazon.com>

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

Signed-off-by: Sudan Landge <sudanl@amazon.com>
Reviewed-by: Alexander Graf <graf@amazon.com>
[Jason: - Small style cleanups and refactoring.]
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/virt/vmgenid.c | 99 +++++++++++++++++++++++++++---------------
 1 file changed, 65 insertions(+), 34 deletions(-)

diff --git a/drivers/virt/vmgenid.c b/drivers/virt/vmgenid.c
index a1c467a0e9f7..0522107f9bee 100644
--- a/drivers/virt/vmgenid.c
+++ b/drivers/virt/vmgenid.c
@@ -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 <Jason@zx2c4.com>");
-- 
2.44.0

[PATCH v8 2/3] dt-bindings: rng: Add vmgenid support

[Jason A. Donenfeld]

From: Sudan Landge <sudanl@amazon.com>

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.

Signed-off-by: Sudan Landge <sudanl@amazon.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Alexander Graf <graf@amazon.com>
Link: https://www.qemu.org/docs/master/specs/vmgenid.html
Link: https://learn.microsoft.com/en-us/windows/win32/hyperv_v2/virtual-machine-generation-identifier
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 .../bindings/rng/microsoft,vmgenid.yaml       | 49 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 2 files changed, 50 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml

diff --git a/Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml b/Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml
new file mode 100644
index 000000000000..8f20dee93e7e
--- /dev/null
+++ b/Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml
@@ -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 <Jason@zx2c4.com>
+
+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>;
+    };
+
+...
diff --git a/MAINTAINERS b/MAINTAINERS
index c23fda1aa1f0..efd8de759d95 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -18469,6 +18469,7 @@ M:	"Theodore Ts'o" <tytso@mit.edu>
 M:	Jason A. Donenfeld <Jason@zx2c4.com>
 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

[PATCH v8 3/3] virt: vmgenid: add support for devicetree bindings

[Jason A. Donenfeld]

From: Sudan Landge <sudanl@amazon.com>

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.

Signed-off-by: Sudan Landge <sudanl@amazon.com>
Reviewed-by: Alexander Graf <graf@amazon.com>
[Jason: - Small style cleanups and refactoring.
        - Re-work ACPI conditionalization. ]
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/virt/Kconfig   |  1 -
 drivers/virt/vmgenid.c | 53 ++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig
index 40129b6f0eca..d8c848cf09a6 100644
--- a/drivers/virt/Kconfig
+++ b/drivers/virt/Kconfig
@@ -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
diff --git a/drivers/virt/vmgenid.c b/drivers/virt/vmgenid.c
index 0522107f9bee..66135eac3abf 100644
--- a/drivers/virt/vmgenid.c
+++ b/drivers/virt/vmgenid.c
@@ -2,12 +2,13 @@
 /*
  * Copyright (C) 2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
  *
- * The "Virtual Machine Generation ID" is exposed via ACPI and changes when a
+ * The "Virtual Machine Generation ID" is exposed via ACPI or DT and changes when a
  * virtual machine forks or is cloned. This driver exists for shepherding that
  * information to random.c.
  */
 
 #include <linux/acpi.h>
+#include <linux/interrupt.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
@@ -41,6 +42,7 @@ static void setup_vmgenid_state(struct vmgenid_state *state, void *virt_addr)
 	add_device_randomness(state->this_id, sizeof(state->this_id));
 }
 
+#ifdef CONFIG_ACPI
 static void vmgenid_acpi_handler(acpi_handle __always_unused handle,
 				 u32 __always_unused event, void *dev)
 {
@@ -92,6 +94,43 @@ static int vmgenid_add_acpi(struct device *dev, struct vmgenid_state *state)
 	ACPI_FREE(parsed.pointer);
 	return ret;
 }
+#else
+static int vmgenid_add_acpi(struct device *dev, struct vmgenid_state *state)
+{
+	return -EINVAL;
+}
+#endif
+
+static irqreturn_t vmgenid_of_irq_handler(int __always_unused irq, void *dev)
+{
+	vmgenid_notify(dev);
+	return IRQ_HANDLED;
+}
+
+static int vmgenid_add_of(struct platform_device *pdev,
+			  struct vmgenid_state *state)
+{
+	void *virt_addr;
+	int ret;
+
+	virt_addr = devm_platform_get_and_ioremap_resource(pdev, 0, NULL);
+	if (IS_ERR(virt_addr))
+		return PTR_ERR(virt_addr);
+
+	setup_vmgenid_state(state, virt_addr);
+
+	ret = platform_get_irq(pdev, 0);
+	if (ret < 0)
+		return ret;
+
+	ret = devm_request_irq(&pdev->dev, ret, vmgenid_of_irq_handler,
+			       IRQF_SHARED, "vmgenid", &pdev->dev);
+	if (ret < 0)
+		return ret;
+
+	pdev->dev.driver_data = state;
+	return 0;
+}
 
 static int vmgenid_add(struct platform_device *pdev)
 {
@@ -103,13 +142,22 @@ static int vmgenid_add(struct platform_device *pdev)
 	if (!state)
 		return -ENOMEM;
 
-	ret = vmgenid_add_acpi(dev, state);
+	if (dev->of_node)
+		ret = vmgenid_add_of(pdev, state);
+	else
+		ret = vmgenid_add_acpi(dev, state);
 
 	if (ret < 0)
 		devm_kfree(dev, state);
 	return ret;
 }
 
+static const struct of_device_id vmgenid_of_ids[] = {
+	{ .compatible = "microsoft,vmgenid", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, vmgenid_of_ids);
+
 static const struct acpi_device_id vmgenid_acpi_ids[] = {
 	{ "VMGENCTR", 0 },
 	{ "VM_GEN_COUNTER", 0 },
@@ -122,6 +170,7 @@ static struct platform_driver vmgenid_plaform_driver = {
 	.driver     = {
 		.name   = "vmgenid",
 		.acpi_match_table = vmgenid_acpi_ids,
+		.of_match_table = vmgenid_of_ids,
 	},
 };
 
-- 
2.44.0

Re: [PATCH v8 0/3] virt: vmgenid: add devicetree bindings support

[Babis Chalios]

On 4/20/24 00:39, Jason A. Donenfeld wrote:
> 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.

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.

Tested-by: Babis Chalios <bchalios@amazon.es>

Cheers,
Babis

Re: [PATCH v8 0/3] virt: vmgenid: add devicetree bindings support

[Jason A. Donenfeld]

Hi Babis,

On Mon, Apr 22, 2024 at 03:29:59PM +0200, Babis Chalios wrote:
> 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.
> 
> Tested-by: Babis Chalios <bchalios@amazon.es>

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