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

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Date:   Thu, 28 Apr 2022 14:10:18 +0000
From:   Sebastian Ene <sebastianene@...gle.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Derek Kiernan <derek.kiernan@...inx.com>,
        Dragan Cvetic <dragan.cvetic@...inx.com>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        qperret@...gle.com, will@...nel.org, maz@...nel.org
Subject: Re: [PATCH v3 2/2] misc: Add a mechanism to detect stalls on guest
 vCPUs

On Mon, Apr 25, 2022 at 09:02:03AM -0700, Randy Dunlap wrote:
> 
> 
> 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

Hi,

> 
> 	                        exits ?
> I dunno, but it's confusing.
> 

Yes, I will correct this typo, thanks for the notice.

> > +	  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

Sebastian