Re: [PATCH v4 2/2] misc: Add a mechanism to detect stalls on guest vCPUs

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Apr 29, 2022 at 08:30:33AM +0000, Sebastian Ene wrote:
> This driver creates per-cpu hrtimers which are required to do the
> periodic 'pet' operation. 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.
> 
> This part of the driver is the 'frontend' which is reponsible for
> delivering the periodic 'pet' events, configuring the virtual peripheral
> and listening for cpu hotplug events. The other part of the driver
> handles the peripheral emulation and this part accounts for lost time by
> looking at the /proc/{}/task/{}/stat entries and is located here:
> https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3548817
> 
> Signed-off-by: Sebastian Ene <sebastianene@google.com>
> ---
>  drivers/misc/Kconfig       |  12 +++
>  drivers/misc/Makefile      |   1 +
>  drivers/misc/vm-watchdog.c | 206 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 219 insertions(+)
>  create mode 100644 drivers/misc/vm-watchdog.c
> 
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 2b9572a6d114..26c3a99e269c 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -493,6 +493,18 @@ config OPEN_DICE
>  
>  	  If unsure, say N.
>  
> +config VM_WATCHDOG
> +	tristate "Virtual Machine Watchdog"
> +	select LOCKUP_DETECTOR
> +	help
> +	  Detect CPU locks on the virtual machine. This driver relies on the
> +	  hrtimers which are CPU-binded to do the 'pet' operation. When a vCPU
> +	  has to do a 'pet', it exits the guest through MMIO write and the
> +	  backend driver takes into account the lost ticks for this particular
> +	  CPU.

There's nothing to keep this tied to a virtual machine at all, right?
You are just relying on some iomem address to be updated, so it should
be a "generic_iomem_watchdog" driver as there's nothing specific to vms
at all from what I can tell.

thanks,

greg k-h