[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.

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

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

 .../devicetree/bindings/watchdog/vm-wdt.yaml  |  44 ++++
 drivers/watchdog/Kconfig                      |   8 +
 drivers/watchdog/Makefile                     |   1 +
 drivers/watchdog/vm-wdt.c                     | 215 ++++++++++++++++++
 4 files changed, 268 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/watchdog/vm-wdt.yaml
 create mode 100644 drivers/watchdog/vm-wdt.c

On Tue, 05 Apr 2022 14:19:54 +0000, Sebastian Ene wrote:
> This watchdog can be used to detect stalls on vCPUs.
> 
> Signed-off-by: Sebastian Ene <sebastianene@google.com>
> ---
>  .../devicetree/bindings/watchdog/vm-wdt.yaml  | 44 +++++++++++++++++++
>  1 file changed, 44 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/watchdog/vm-wdt.yaml
> 

My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
on your patch (DT_CHECKER_FLAGS is new in v5.13):

yamllint warnings/errors:

dtschema/dtc warnings/errors:
/builds/robherring/linux-dt-review/Documentation/devicetree/bindings/watchdog/vm-wdt.yaml: properties:timeout-sec: '$ref' should not be valid under {'const': '$ref'}
	hint: Standard unit suffix properties don't need a type $ref
	from schema $id: http://devicetree.org/meta-schemas/core.yaml#
/builds/robherring/linux-dt-review/Documentation/devicetree/bindings/watchdog/vm-wdt.yaml: ignoring, error in schema: properties: timeout-sec
Documentation/devicetree/bindings/watchdog/vm-wdt.example.dtb:0:0: /example-0/watchdog: failed to match any schema with compatible: ['qemu,vm-watchdog']

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/patch/

This check can fail if there are any dependencies. The base for a patch
series is generally the most recent rc1.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit.

On Wed, Apr 06, 2022 at 07:25:24AM -0500, Rob Herring wrote:
> On Tue, 05 Apr 2022 14:19:54 +0000, Sebastian Ene wrote:
> > This watchdog can be used to detect stalls on vCPUs.
> > 
> > Signed-off-by: Sebastian Ene <sebastianene@google.com>
> > ---
> >  .../devicetree/bindings/watchdog/vm-wdt.yaml  | 44 +++++++++++++++++++
> >  1 file changed, 44 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/watchdog/vm-wdt.yaml
> > 

Hello Rob,

> 
> My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
> on your patch (DT_CHECKER_FLAGS is new in v5.13):
> 
> yamllint warnings/errors:
> 
> dtschema/dtc warnings/errors:
> /builds/robherring/linux-dt-review/Documentation/devicetree/bindings/watchdog/vm-wdt.yaml: properties:timeout-sec: '$ref' should not be valid under {'const': '$ref'}
> 	hint: Standard unit suffix properties don't need a type $ref
> 	from schema $id: http://devicetree.org/meta-schemas/core.yaml#
> /builds/robherring/linux-dt-review/Documentation/devicetree/bindings/watchdog/vm-wdt.yaml: ignoring, error in schema: properties: timeout-sec
> Documentation/devicetree/bindings/watchdog/vm-wdt.example.dtb:0:0: /example-0/watchdog: failed to match any schema with compatible: ['qemu,vm-watchdog']
> 
> doc reference errors (make refcheckdocs):
> 
> See https://patchwork.ozlabs.org/patch/
> 

I will fix them, thanks for letting me know.

> This check can fail if there are any dependencies. The base for a patch
> series is generally the most recent rc1.
> 
> If you already ran 'make dt_binding_check' and didn't see the above
> error(s), then make sure 'yamllint' is installed and dt-schema is up to
> date:
> 
> pip3 install dtschema --upgrade
> 
> Please check and re-submit.
> 

Cheers,
Sebastian