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Date:   Thu, 16 Jun 2022 16:03:10 +0000
From:   Sebastian Ene <sebastianene@google.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Rob Herring <robh+dt@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Dragan Cvetic <dragan.cvetic@xilinx.com>,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        maz@kernel.org, will@kernel.org, vdonnefort@google.com,
        Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH v6 2/2] misc: Add a mechanism to detect stalls on guest
 vCPUs
Message-ID: <YqtUPh/9qK7+jqJc@google.com>
References: <20220616092737.1713667-1-sebastianene@google.com>
 <20220616092737.1713667-3-sebastianene@google.com>
 <YqsBeme1Vnzj5k7+@kroah.com>
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On Thu, Jun 16, 2022 at 12:10:02PM +0200, Greg Kroah-Hartman wrote:
> On Thu, Jun 16, 2022 at 09:27:39AM +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
> > 
> > Reported-by: kernel test robot <lkp@intel.com>
> > Signed-off-by: Sebastian Ene <sebastianene@google.com>
> > ---
> >  drivers/misc/Kconfig               |  12 ++
> >  drivers/misc/Makefile              |   1 +
> >  drivers/misc/vcpu_stall_detector.c | 222 +++++++++++++++++++++++++++++
> >  3 files changed, 235 insertions(+)
> >  create mode 100644 drivers/misc/vcpu_stall_detector.c
> > 
> > diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> > index 41d2bb0ae23a..9b3cb5dfd5a7 100644
> > --- a/drivers/misc/Kconfig
> > +++ b/drivers/misc/Kconfig
> > @@ -483,6 +483,18 @@ config OPEN_DICE
> >  
> >  	  If unsure, say N.
> >  
> > +config VCPU_STALL_DETECTOR
> > +	tristate "VCPU stall detector"
> > +	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.

Hi,

> 
> which virtual machine framework is this for?  kvm?  xen?  hyperv?
> vmware?  something else?
> 
> Specifics please...
> 
> thanks,

I will improve my description, thanks for taking a look.

> 
> greg k-h

Seb