linux-kernel - Re: [PATCH v3 2/2] misc: Add a mechanism to detect stalls on guest vCPUs

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Message-ID: <1d938867-05b9-fab5-1f48-a635d92420d3@infradead.org>
Date:   Mon, 25 Apr 2022 09:02:03 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Sebastian Ene <sebastianene@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Dragan Cvetic <dragan.cvetic@...inx.com>
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        maz@...nel.org, will@...nel.org, qperret@...gle.com
Subject: Re: [PATCH v3 2/2] misc: Add a mechanism to detect stalls on guest
 vCPUs



On 4/25/22 06:42, 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@...gle.com>
> ---
>  drivers/misc/Kconfig  |  12 +++
>  drivers/misc/Makefile |   1 +
>  drivers/misc/vm-wdt.c | 207 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 220 insertions(+)
>  create mode 100644 drivers/misc/vm-wdt.c
> 
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 2b9572a6d114..71c173e3f064 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 exists the guest through MMIO write and the

	                        exits ?
I dunno, but it's confusing.

> +	  backend driver takes into account the lost ticks for this particular
> +	  CPU.
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called vm-wdt.



-- 
~Randy