[v4,0/2] Detect stalls on guest vCPUS

This adds a mechanism to detect stalls on the guest vCPUS by creating a
per CPU hrtimer which periodically 'pets' the host backend driver.
On a conventional watchdog-core driver, the userspace is responsible for
delivering the 'pet' events by writing to the particular /dev/watchdogN node.
In this case we require a strong thread affinity to be able to
account for lost time on a per vCPU basis.

This device driver acts as a soft lockup detector by relying on the host
backend driver to measure the elapesed time between subsequent 'pet' events.
If the elapsed time doesn't match an expected value, the backend driver
decides that the guest vCPU is locked and resets the guest. The host
backend driver takes into account the time that the guest is not
running. The communication with the backend driver is done through MMIO
and the register layout of the virtual watchdog is described as part of
the backend driver changes.

The host backend driver is implemented as part of:
https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3548817

Changelog v4:
 - rename the source from vm-wdt.c -> vm-watchdog.c
 - convert all the error logging calls from pr_* to dev_* calls
 - rename the DTS node "clock" to "clock-frequency"

Changelog v3:
 - cosmetic fixes, remove pr_info and version information
 - improve description in the commit messag
 - improve description in the Kconfig help section

Sebastian Ene (2):
  dt-bindings: vm-wdt: Add qemu,vm-watchdog compatible
  misc: Add a mechanism to detect stalls on guest vCPUs

 .../devicetree/bindings/misc/vm-watchdog.yaml |  45 ++++
 drivers/misc/Kconfig                          |  12 +
 drivers/misc/Makefile                         |   1 +
 drivers/misc/vm-watchdog.c                    | 206 ++++++++++++++++++
 4 files changed, 264 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/misc/vm-watchdog.yaml
 create mode 100644 drivers/misc/vm-watchdog.c

On Fri, Apr 29, 2022 at 08:30:31AM +0000, Sebastian Ene wrote:
> The stall detection mechanism allows to configure the expiration
> duration and the internal counter clock frequency measured in Hz.
> Add these properties in the schema.
> 
> Signed-off-by: Sebastian Ene <sebastianene@google.com>
> ---
>  .../devicetree/bindings/misc/vm-watchdog.yaml | 45 +++++++++++++++++++
>  1 file changed, 45 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/misc/vm-watchdog.yaml
> 
> diff --git a/Documentation/devicetree/bindings/misc/vm-watchdog.yaml b/Documentation/devicetree/bindings/misc/vm-watchdog.yaml
> new file mode 100644
> index 000000000000..d7cca23357ab
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/misc/vm-watchdog.yaml
> @@ -0,0 +1,45 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/misc/vm-watchdog.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: VM watchdog
> +
> +description: |
> +  This binding describes a CPU stall detector mechanism for virtual cpus
> +  which is accessed through MMIO.
> +
> +maintainers:
> +  - Sebastian Ene <sebastianene@google.com>
> +
> +properties:
> +  compatible:
> +    enum:
> +      - qemu,vm-watchdog
> +  clock-frequency:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description: |
> +      The watchdog internal clock measure in Hz used to decrement the
> +      watchdog counter register on each tick.
> +      Defaults to 10 if unset.
> +  timeout-sec:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description: |
> +      The watchdog expiration timeout measured in seconds.
> +      Defaults to 8 if unset.
> +
> +required:
> +  - compatible
> +
> +additionalProperties: false

Hi,

> +
> +examples:
> +  - |
> +    watchdog {
> +      compatible = "qemu,vm-watchdog";
> +      clock-frequency = <10>;
> +      timeout-sec = <8>;
> +    };
> +
> +...
> -- 
> 2.36.0.464.gb9c8b46e94-goog
>

I was thinking to move the properties clock-frequency and timeout-sec as
part of the emulated watchdog registers and keep only the registers
property in the DT.

Thanks,
Seb