misc: Add a mechanism to detect stalls on guest vCPUs

misc: Add a mechanism to detect stalls on guest vCPUs

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 is
an emulated MMIO device which is part of the KVM virtual machine
monitor and this part accounts for lost time by looking at the
/proc/{}/task/{}/stat entries.

Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Will Deacon <will@kernel.org>
Signed-off-by: Sebastian Ene <sebastianene@google.com>
Link: https://lore.kernel.org/r/20220711081720.2870509-3-sebastianene@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>